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/database/queries/queries.sql

@@ -16,7 +16,7 @@ SELECT id, email, username, theme, first_name, last_name, role, created_at, upda
 SELECT id, email, username, password_hash, theme, first_name, last_name, role, created_at, updated_at FROM users WHERE email = $1 OR username = $1;
 
 -- name: GetUser :one
-SELECT 
+SELECT
     u.id,
     u.email,
     u.username,
@@ -35,7 +35,7 @@ WHERE u.id = $1;
 SELECT password_hash FROM users WHERE id = $1;
 
 -- name: ListUsers :many
-SELECT 
+SELECT
     u.id,
     u.email,
     u.username,
@@ -520,7 +520,7 @@ UPDATE refresh_tokens SET revoked_at = NOW() WHERE user_id = $1 AND revoked_at I
 DELETE FROM refresh_tokens WHERE expires_at < NOW() OR (revoked_at IS NOT NULL AND revoked_at < NOW() - INTERVAL '7 days');
 
 -- ============================================
--- PHASE 1: FORMAT DETECTION & PROGRESS (Week 2)
+-- FORMAT DETECTION & PROGRESS
 -- ============================================
 
 -- Update media item format group information
@@ -716,7 +716,7 @@ SELECT
  LIMIT $2;
 
  -- ============================================
--- PHASE 2: DEVICE MANAGEMENT & AUTH (Weeks 5-6)
+-- DEVICE MANAGEMENT & AUTH
 -- ============================================
 
 -- Device Registration & Management
@@ -837,7 +837,7 @@ ORDER BY priority ASC, created_at ASC;
 UPDATE sync_queue
 SET
     attempts = attempts + 1,
-    status = CASE 
+    status = CASE
         WHEN attempts + 1 >= max_attempts THEN 'failed'
         ELSE 'pending'
     END,
@@ -856,7 +856,7 @@ FROM sync_queue
 WHERE device_id = $1;
 
 -- name: ListAllSyncQueueItems :many
-SELECT 
+SELECT
     sq.*,
     d.device_name,
     d.device_type,
@@ -870,8 +870,8 @@ ORDER BY sq.priority ASC, sq.created_at DESC
 LIMIT $1 OFFSET $2;
 
 -- name: GetNextRetryTime :one
-SELECT 
-    CASE 
+SELECT
+    CASE
         WHEN attempts = 0 THEN NOW()
         WHEN attempts = 1 THEN NOW() + INTERVAL '1 minute'
         WHEN attempts = 2 THEN NOW() + INTERVAL '5 minutes'
@@ -929,7 +929,7 @@ DELETE FROM sync_conflicts WHERE id = $1;
  ORDER BY sc.created_at DESC;
 
 -- ============================================
--- PHASE 3: KOREADER SYNC PROTOCOL (Weeks 7-9)
+-- KOREADER SYNC PROTOCOL
 -- ============================================
 
 -- name: GetMediaItemByFilePathForSync :one
@@ -1040,7 +1040,7 @@ WHERE media_item_id = $1
   AND last_sync_source != $3;
 
 -- ============================================
--- KOBO SHELF MANAGEMENT QUERIES (Phase 4)
+-- KOBO SHELF MANAGEMENT QUERIES
 -- ============================================
 
 -- name: AddBookToKoboShelf :one
@@ -1093,7 +1093,7 @@ FROM kobo_shelves
 WHERE device_id = $1;
 
 -- ============================================
--- KOBO ENTITLEMENT QUERIES (Phase 4)
+-- KOBO ENTITLEMENT QUERIES
 -- ============================================
 
 -- name: CreateOrUpdateKoboEntitlement :one
@@ -1161,7 +1161,7 @@ SELECT * FROM media_items WHERE kobo_content_id = $1;
 -- Media Items Admin Operations
 
 -- ============================================
--- PHASE 1: UNIVERSAL BOOK IDENTIFIERS (Week 1)
+-- UNIVERSAL BOOK IDENTIFIERS
 -- ============================================
 
 -- Update media item with universal identifiers
@@ -1522,7 +1522,7 @@ WHERE ks.device_id = $1 AND ks.collection_id = $2
 ORDER BY ks.position_in_collection ASC, ks.shelf_position ASC;
 
 -- ============================================
--- PHASE 6: ENHANCED KOBO SYNC (Week 3-4)
+-- ENHANCED KOBO SYNC
 -- ============================================
 
 -- Create unlinked book entry
@@ -1587,4 +1587,4 @@ FROM unlinked_books ub
 JOIN devices d ON ub.device_id = d.id
 WHERE ub.resolved = false
 ORDER BY ub.last_seen_at DESC
-LIMIT $1 OFFSET $2;
+LIMIT $1 OFFSET $2;