refactor: extract CSS modules for session/settings and delete styles.css (Task 2.3)

- Create InstanceList.module.css, AppShell.module.css, SettingsTabLayout.module.css
- Create CommitPanel.module.css, FileViewer.module.css
- Create page CSS files: sessions, repo-workspace, dashboard, projects,
  git-history, ssh-keys, settings
- Update components to import and use CSS modules
- Delete monolithic styles.css (2,255 lines)
- Update main.tsx to import page CSS and new modules

Quality gates: tsc (pass), eslint (pass), build (pass)
Refs: repo-restructure Task 2.3

apps/api/src/services/config_profiles.py

@@ -0,0 +1,81 @@
+"""Config profile business logic."""
+
+import logging
+import uuid
+
+from fastapi import HTTPException, status
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from src.models.config_include import ConfigInclude
+from src.models.config_mount import ConfigMount
+from src.models.config_profile import ConfigProfile
+from src.models.tool_type import ToolType
+from src.models.user_config import UserConfig
+
+logger = logging.getLogger(__name__)
+
+MAX_INCLUDES_DEPTH = 10
+
+
+async def get_owned_profile(
+    profile_id: uuid.UUID,
+    user_id: uuid.UUID,
+    session: AsyncSession,
+) -> ConfigProfile:
+    """Fetch a config profile and verify ownership."""
+    profile = await session.get(ConfigProfile, profile_id)
+    if profile is None or profile.user_id != user_id:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="config profile not found",
+        )
+    return profile
+
+
+async def _detect_cycle(
+    session: AsyncSession,
+    profile_id: uuid.UUID,
+    visited: set[uuid.UUID] | None = None,
+    depth: int = 0,
+) -> bool:
+    """Detect cycles in profile includes using DFS.
+
+    Returns True if a cycle is detected.
+    """
+    if depth > MAX_INCLUDES_DEPTH:
+        return True
+
+    if visited is None:
+        visited = set()
+
+    if profile_id in visited:
+        return True
+
+    visited.add(profile_id)
+
+    result = await session.execute(
+        select(ConfigInclude.included_profile_id).where(
+            ConfigInclude.profile_id == profile_id
+        )
+    )
+    included_ids = result.scalars().all()
+
+    for included_id in included_ids:
+        if await _detect_cycle(session, included_id, visited.copy(), depth + 1):
+            return True
+
+    return False
+
+
+async def validate_includes_no_cycle(
+    session: AsyncSession,
+    profile_id: uuid.UUID,
+    new_included_id: uuid.UUID | None = None,
+) -> None:
+    """Validate that adding an include wouldn't create a cycle."""
+    if new_included_id and await _detect_cycle(session, new_included_id, {profile_id}):
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="adding this include would create a circular reference",
+        )