refactor: remove Phase X terminology from source code comments

Remove planning document phase references from code comments:

app_test.go:
- Remove Phase 5 references from 8 test function comments

querier.go & queries.sql.go:
- Remove Phase 1, 2, 3, 4, 6 references from section headers
- Clean up week numbers (Weeks 5-6, Week 3-4, etc.)

queries.sql:
- Remove Phase 4 references from Kobo queries

kobo.go:
- Remove Phase 6 references from ContentId mapping comments

progress.go:
- Remove Phase 1 reference from route comment

media_scanner.go & media_scanner_library_type_test.go:
- Remove Phase 2 references from library type scanning comments

schema.sql:
- Remove Phase 1, 2, 3, 4, 5, 7 references from table/section comments
- Clean up: Format Detection, Progress Tracking, Device Registry,
  Sync Queue, Conflict Resolution, Reading History, Indexes, etc.

test_helpers.go:
- Remove Phase 6 reference from handler setup comment

These phase numbers were from internal planning documents and have no
meaning in the codebase. Removing them makes the code self-documenting.

internal/router/progress.go

@@ -11,7 +11,7 @@ func registerProgressRoutes(cfg *Config, scannerHandler *handlers.Handler) {
 	jwtMiddleware := createJWTMiddleware(cfg)
 	protected := e.Group("/api", jwtMiddleware)
 
-	// Universal Progress routes (Phase 1)
+	// Universal Progress routes
 	protected.GET("/progress/:id", scannerHandler.GetUniversalProgress)
 	protected.POST("/progress/:id", scannerHandler.UpdateUniversalProgress)
 	protected.GET("/progress/:id/history", scannerHandler.GetProgressHistory)