perf(upload): optimize file hot paths and incremental admin stats

- Use RWMutex for disk cache reads and singleflight for WebP cache misses
- Cache migration read-only state and file access whitelist with pub/sub invalidation
- Add w_upload_stats incremental counters updated on upload/delete
- Add w_uploads composite indexes and goose backfill migrations
- Document performance analysis in docs/PERFORMANCE.md
- Fix RegisterCustomRoutes to accept apiV1Router parameter

internal/db/migrator/goose/postgres/202606170001_add_upload_composite_indexes.sql

@@ -0,0 +1,9 @@
+-- +goose Up
+CREATE INDEX IF NOT EXISTS idx_w_uploads_status_created_at ON w_uploads (status, created_at);
+CREATE INDEX IF NOT EXISTS idx_w_uploads_storage_driver_status ON w_uploads (storage_driver, status);
+CREATE INDEX IF NOT EXISTS idx_w_uploads_hash_file_size_status ON w_uploads (hash, file_size, status);
+
+-- +goose Down
+DROP INDEX IF EXISTS idx_w_uploads_hash_file_size_status;
+DROP INDEX IF EXISTS idx_w_uploads_storage_driver_status;
+DROP INDEX IF EXISTS idx_w_uploads_status_created_at;

internal/db/migrator/goose/postgres/202606170002_create_upload_stats_table.sql

@@ -0,0 +1,12 @@
+-- +goose Up
+CREATE TABLE IF NOT EXISTS w_upload_stats (
+    dimension VARCHAR(32) NOT NULL,
+    stat_key VARCHAR(64) NOT NULL DEFAULT '',
+    file_count BIGINT NOT NULL DEFAULT 0,
+    file_size BIGINT NOT NULL DEFAULT 0,
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    PRIMARY KEY (dimension, stat_key)
+);
+
+-- +goose Down
+DROP TABLE IF EXISTS w_upload_stats;

internal/db/migrator/goose/postgres/202606170003_backfill_upload_stats.sql

@@ -0,0 +1,67 @@
+-- +goose Up
+INSERT INTO w_upload_stats (dimension, stat_key, file_count, file_size)
+SELECT 'total', '', COUNT(*), COALESCE(SUM(file_size), 0)
+FROM w_uploads
+WHERE status != 'deleted'
+ON CONFLICT (dimension, stat_key) DO UPDATE SET
+    file_count = EXCLUDED.file_count,
+    file_size = EXCLUDED.file_size,
+    updated_at = CURRENT_TIMESTAMP;
+
+INSERT INTO w_upload_stats (dimension, stat_key, file_count, file_size)
+SELECT
+    'type',
+    COALESCE(NULLIF(type, ''), 'generic'),
+    COUNT(*),
+    COALESCE(SUM(file_size), 0)
+FROM w_uploads
+WHERE status != 'deleted'
+GROUP BY COALESCE(NULLIF(type, ''), 'generic')
+ON CONFLICT (dimension, stat_key) DO UPDATE SET
+    file_count = EXCLUDED.file_count,
+    file_size = EXCLUDED.file_size,
+    updated_at = CURRENT_TIMESTAMP;
+
+INSERT INTO w_upload_stats (dimension, stat_key, file_count, file_size)
+SELECT
+    'category',
+    CASE
+        WHEN LOWER(mime_type) LIKE 'image/%'
+            OR LOWER(extension) IN ('jpg', 'jpeg', 'png', 'webp', 'gif') THEN '图片'
+        WHEN LOWER(mime_type) LIKE 'video/%' THEN '视频'
+        WHEN LOWER(mime_type) LIKE 'audio/%' THEN '音频'
+        WHEN LOWER(extension) IN ('zip', 'rar', '7z', 'tar', 'gz', 'tgz', 'bz2', 'xz')
+            OR LOWER(mime_type) LIKE '%zip%'
+            OR LOWER(mime_type) LIKE '%tar%'
+            OR LOWER(mime_type) LIKE '%gzip%' THEN '压缩包'
+        WHEN LOWER(extension) IN ('pdf', 'doc', 'docx', 'xls', 'xlsx', 'ppt', 'pptx', 'txt', 'md', 'csv', 'json', 'yaml', 'yml', 'xml')
+            OR LOWER(mime_type) LIKE 'text/%'
+            OR LOWER(mime_type) = 'application/pdf' THEN '文档'
+        ELSE '其他'
+    END,
+    COUNT(*),
+    COALESCE(SUM(file_size), 0)
+FROM w_uploads
+WHERE status != 'deleted'
+GROUP BY 2
+ON CONFLICT (dimension, stat_key) DO UPDATE SET
+    file_count = EXCLUDED.file_count,
+    file_size = EXCLUDED.file_size,
+    updated_at = CURRENT_TIMESTAMP;
+
+INSERT INTO w_upload_stats (dimension, stat_key, file_count, file_size)
+SELECT
+    'trend',
+    TO_CHAR(created_at, 'YYYY-MM-DD'),
+    COUNT(*),
+    COALESCE(SUM(file_size), 0)
+FROM w_uploads
+WHERE status != 'deleted'
+GROUP BY TO_CHAR(created_at, 'YYYY-MM-DD')
+ON CONFLICT (dimension, stat_key) DO UPDATE SET
+    file_count = EXCLUDED.file_count,
+    file_size = EXCLUDED.file_size,
+    updated_at = CURRENT_TIMESTAMP;
+
+-- +goose Down
+DELETE FROM w_upload_stats;

internal/db/migrator/goose/sqlite/202606170001_add_upload_composite_indexes.sql

@@ -0,0 +1,9 @@
+-- +goose Up
+CREATE INDEX IF NOT EXISTS idx_w_uploads_status_created_at ON w_uploads (status, created_at);
+CREATE INDEX IF NOT EXISTS idx_w_uploads_storage_driver_status ON w_uploads (storage_driver, status);
+CREATE INDEX IF NOT EXISTS idx_w_uploads_hash_file_size_status ON w_uploads (hash, file_size, status);
+
+-- +goose Down
+DROP INDEX IF EXISTS idx_w_uploads_hash_file_size_status;
+DROP INDEX IF EXISTS idx_w_uploads_storage_driver_status;
+DROP INDEX IF EXISTS idx_w_uploads_status_created_at;

internal/db/migrator/goose/sqlite/202606170002_create_upload_stats_table.sql

@@ -0,0 +1,12 @@
+-- +goose Up
+CREATE TABLE IF NOT EXISTS w_upload_stats (
+    dimension VARCHAR(32) NOT NULL,
+    stat_key VARCHAR(64) NOT NULL DEFAULT '',
+    file_count BIGINT NOT NULL DEFAULT 0,
+    file_size BIGINT NOT NULL DEFAULT 0,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    PRIMARY KEY (dimension, stat_key)
+);
+
+-- +goose Down
+DROP TABLE IF EXISTS w_upload_stats;

internal/db/migrator/goose/sqlite/202606170003_backfill_upload_stats.sql

@@ -0,0 +1,67 @@
+-- +goose Up
+INSERT INTO w_upload_stats (dimension, stat_key, file_count, file_size)
+SELECT 'total', '', COUNT(*), COALESCE(SUM(file_size), 0)
+FROM w_uploads
+WHERE status != 'deleted'
+ON CONFLICT (dimension, stat_key) DO UPDATE SET
+    file_count = excluded.file_count,
+    file_size = excluded.file_size,
+    updated_at = CURRENT_TIMESTAMP;
+
+INSERT INTO w_upload_stats (dimension, stat_key, file_count, file_size)
+SELECT
+    'type',
+    COALESCE(NULLIF(type, ''), 'generic'),
+    COUNT(*),
+    COALESCE(SUM(file_size), 0)
+FROM w_uploads
+WHERE status != 'deleted'
+GROUP BY COALESCE(NULLIF(type, ''), 'generic')
+ON CONFLICT (dimension, stat_key) DO UPDATE SET
+    file_count = excluded.file_count,
+    file_size = excluded.file_size,
+    updated_at = CURRENT_TIMESTAMP;
+
+INSERT INTO w_upload_stats (dimension, stat_key, file_count, file_size)
+SELECT
+    'category',
+    CASE
+        WHEN LOWER(mime_type) LIKE 'image/%'
+            OR LOWER(extension) IN ('jpg', 'jpeg', 'png', 'webp', 'gif') THEN '图片'
+        WHEN LOWER(mime_type) LIKE 'video/%' THEN '视频'
+        WHEN LOWER(mime_type) LIKE 'audio/%' THEN '音频'
+        WHEN LOWER(extension) IN ('zip', 'rar', '7z', 'tar', 'gz', 'tgz', 'bz2', 'xz')
+            OR LOWER(mime_type) LIKE '%zip%'
+            OR LOWER(mime_type) LIKE '%tar%'
+            OR LOWER(mime_type) LIKE '%gzip%' THEN '压缩包'
+        WHEN LOWER(extension) IN ('pdf', 'doc', 'docx', 'xls', 'xlsx', 'ppt', 'pptx', 'txt', 'md', 'csv', 'json', 'yaml', 'yml', 'xml')
+            OR LOWER(mime_type) LIKE 'text/%'
+            OR LOWER(mime_type) = 'application/pdf' THEN '文档'
+        ELSE '其他'
+    END,
+    COUNT(*),
+    COALESCE(SUM(file_size), 0)
+FROM w_uploads
+WHERE status != 'deleted'
+GROUP BY 2
+ON CONFLICT (dimension, stat_key) DO UPDATE SET
+    file_count = excluded.file_count,
+    file_size = excluded.file_size,
+    updated_at = CURRENT_TIMESTAMP;
+
+INSERT INTO w_upload_stats (dimension, stat_key, file_count, file_size)
+SELECT
+    'trend',
+    STRFTIME('%Y-%m-%d', created_at),
+    COUNT(*),
+    COALESCE(SUM(file_size), 0)
+FROM w_uploads
+WHERE status != 'deleted'
+GROUP BY STRFTIME('%Y-%m-%d', created_at)
+ON CONFLICT (dimension, stat_key) DO UPDATE SET
+    file_count = excluded.file_count,
+    file_size = excluded.file_size,
+    updated_at = CURRENT_TIMESTAMP;
+
+-- +goose Down
+DELETE FROM w_upload_stats;