Add Renderers page for L1 server management

- Add user_renderers table to track which L1 servers users are attached to
- Add L1_SERVERS config to define available renderers
- Add /renderers page showing attachment status for each L1 server
- Add attach functionality (redirects to L1 /auth with token)
- Add detach functionality with HTMX updates
- Add Renderers link to nav bar

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

db.py

@@ -100,6 +100,15 @@ CREATE TABLE IF NOT EXISTS followers (
     UNIQUE(username, acct)
 );
 
+-- User's attached L1 renderers
+CREATE TABLE IF NOT EXISTS user_renderers (
+    id SERIAL PRIMARY KEY,
+    username VARCHAR(255) NOT NULL REFERENCES users(username),
+    l1_url TEXT NOT NULL,
+    attached_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    UNIQUE(username, l1_url)
+);
+
 -- Indexes
 CREATE INDEX IF NOT EXISTS idx_users_created_at ON users(created_at);
 CREATE INDEX IF NOT EXISTS idx_assets_content_hash ON assets(content_hash);
@@ -715,3 +724,40 @@ async def get_anchor_stats() -> dict:
             "anchored_activities": anchored_activities,
             "unanchored_activities": unanchored_activities
         }
+
+
+# ============ User Renderers (L1 attachments) ============
+
+async def get_user_renderers(username: str) -> list[str]:
+    """Get L1 renderer URLs attached by a user."""
+    async with get_connection() as conn:
+        rows = await conn.fetch(
+            "SELECT l1_url FROM user_renderers WHERE username = $1 ORDER BY attached_at",
+            username
+        )
+        return [row["l1_url"] for row in rows]
+
+
+async def attach_renderer(username: str, l1_url: str) -> bool:
+    """Attach a user to an L1 renderer. Returns True if newly attached."""
+    async with get_connection() as conn:
+        try:
+            await conn.execute(
+                """INSERT INTO user_renderers (username, l1_url)
+                   VALUES ($1, $2)
+                   ON CONFLICT (username, l1_url) DO NOTHING""",
+                username, l1_url
+            )
+            return True
+        except Exception:
+            return False
+
+
+async def detach_renderer(username: str, l1_url: str) -> bool:
+    """Detach a user from an L1 renderer. Returns True if was attached."""
+    async with get_connection() as conn:
+        result = await conn.execute(
+            "DELETE FROM user_renderers WHERE username = $1 AND l1_url = $2",
+            username, l1_url
+        )
+        return "DELETE 1" in result