refactor(repo): consolidate openflare-server to root and move subprojects to internal/apps

- Merge all files inside openflare-server to the repository root directory.
- Relocate agent, relay, and flared subprojects from internal/ to internal/apps/.
- Combine docker-compose files and update build context paths to root.
- Update GitHub workflows and Dockerfiles to refer to new directories and package names.
- Rewrite Go package imports across all files.
- Resolve database renew test race condition and clean up docs.

docker/Dockerfile.flared

@@ -0,0 +1,30 @@
+# syntax=docker/dockerfile:1.7
+ARG VERSION=dev
+
+FROM golang:1.25-alpine AS builder
+
+ARG VERSION
+
+WORKDIR /build
+COPY go.mod go.sum ./
+RUN --mount=type=cache,target=/go/pkg/mod \
+    go mod download
+
+COPY . .
+RUN --mount=type=cache,target=/go/pkg/mod \
+    --mount=type=cache,target=/root/.cache/go-build \
+    CGO_ENABLED=0 GOOS=linux go build -trimpath -ldflags "-s -w -X 'github.com/Rain-kl/Wavelet/internal/apps/flared/config.Version=$VERSION'" -o flared ./cmd/flared/main.go
+
+# Final runtime image
+FROM fatedier/frpc:v0.69.0
+
+WORKDIR /app
+
+# Copy openflared binary
+COPY --from=builder /build/flared .
+
+ENV OPENFLARE_DATA_DIR=/app/data
+ENV OPENFLARE_FRPC_PATH=/usr/bin/frpc
+
+ENTRYPOINT ["/app/flared"]
+CMD []