autoresearch iter 22: delete lint suppressions that suppress nothing

24 of the 96 nolint directives were dead: they covered findings that no
longer exist. A stale suppression is not inert — it silently claims any
future finding for that linter in that scope, so a real problem raised
there would vanish without anyone noticing. Explanatory prose was kept as
ordinary comments.

Two directives proved load-bearing under the project gate even though
nolintlint reported them unused, and removing them exposed verified
contextcheck false positives: App.Run does forward a sigCtx derived from
the caller's context to Start, and the migration lock renewal must keep
its own deadline because the task context may already be canceled. Both
were restored, narrowed to the live linter, and given the reason the
originals lacked.

backend/core/app.go

@@ -303,8 +303,6 @@ func (a *App) RunMigrations() error {
 // 2. Dispatches database migrations via MigrationEngine.
 // 3. Filters and starts drivers matching the active Profile.
 // 4. Emits "app:ready" on the EventBus.
-//
-//nolint:contextcheck
 func (a *App) Start(ctx ...context.Context) error {
 	a.mu.Lock()
 	if a.running {
@@ -386,8 +384,6 @@ func (a *App) Start(ctx ...context.Context) error {
 // 2. Stops all started drivers in LIFO (reverse) order.
 // 3. Disposes the Context (running registered OnDispose callbacks in LIFO order).
 // 4. Emits "app:stopped" on the EventBus.
-//
-//nolint:contextcheck
 func (a *App) Stop(ctx ...context.Context) error {
 	a.mu.Lock()
 	if !a.running {
@@ -448,7 +444,7 @@ func (a *App) Stop(ctx ...context.Context) error {
 // Run starts the application and blocks until an OS signal (SIGINT, SIGTERM) or context cancellation is received,
 // then executes graceful shutdown.
 //
-//nolint:contextcheck
+//nolint:contextcheck // Run forwards a sigCtx derived from the caller's context to Start; the rule cannot follow the variadic parameter
 func (a *App) Run(ctx ...context.Context) error {
 	var parent context.Context
 	switch {
@@ -505,8 +501,6 @@ func (a *App) ExecuteCLI(args ...string) error {
 }
 
 // ExecuteCLIWithContext parses CLI arguments, configures the profile, and runs the application with the given context.
-//
-//nolint:contextcheck
 func (a *App) ExecuteCLIWithContext(ctx context.Context, args ...string) error {
 	cliArgs := args
 	if len(cliArgs) == 0 {