feat: workspaces system — create, select, rename, delete workspaces

- DB: pages.workspace_id column linking pages to workspaces table
- /workspaces: list, create, rename, delete workspaces page
- API: GET/POST/PUT/DELETE /api/workspaces + POST select
- Session: flowdeck_workspace cookie for active workspace tracking
- Sidebar: Workspace section shows active workspace name + page tree
- Local workspace APIs filter by active workspace_id
- Home redirects non-Gitea users to /workspaces

app/db.py

@@ -152,6 +152,7 @@ def init_db():
             CREATE TABLE IF NOT EXISTS pages (
                 id INTEGER PRIMARY KEY AUTOINCREMENT,
                 workspace TEXT NOT NULL,
+                workspace_id INTEGER REFERENCES workspaces(id),
                 title TEXT NOT NULL DEFAULT 'New page',
                 content TEXT NOT NULL DEFAULT '',
                 parent_section TEXT DEFAULT 'Private',
@@ -322,6 +323,10 @@ def init_db():
             conn.execute("ALTER TABLE pages ADD COLUMN published INTEGER DEFAULT 0")
         except sqlite3.OperationalError:
             pass
+        try:
+            conn.execute("ALTER TABLE pages ADD COLUMN workspace_id INTEGER REFERENCES workspaces(id)")
+        except sqlite3.OperationalError:
+            pass
         # v2.2: Auth locale
         for col in ["password_hash", "is_active", "last_login", "login_attempts", "locked_until"]:
             try: