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/git/control.py

@@ -0,0 +1,196 @@
+"""Git control operations with repo validation."""
+
+import logging
+import os
+import uuid
+
+from fastapi import HTTPException, status
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from src.models.git_repository import GitRepository
+from src.models.user import User
+from src.schemas.git_repository import (
+    BranchCreateRequest,
+    CheckoutRequest,
+    CommitRequest,
+    FetchResponse,
+    MergeRequest,
+    MergeResponse,
+    PullResponse,
+    PushResponse,
+    StatusResponse,
+)
+from src.services.git.repository import ensure_repo_on_disk, get_repo_and_validate
+from src.utils.git_control import (
+    checkout_branch,
+    commit_changes,
+    create_branch,
+    delete_branch,
+    fetch,
+    get_status,
+    merge,
+    pull,
+    push,
+)
+
+logger = logging.getLogger(__name__)
+
+
+async def get_status_with_validation(
+    session: AsyncSession,
+    project_id: uuid.UUID,
+    repo_id: uuid.UUID,
+) -> StatusResponse:
+    repo = await get_repo_and_validate(session, repo_id, project_id)
+    ensure_repo_on_disk(repo)
+    try:
+        result = get_status(repo.path)
+        return StatusResponse(
+            branch=result.branch,
+            modified=result.modified,
+            added=result.added,
+            deleted=result.deleted,
+            untracked=result.untracked,
+            renamed=result.renamed,
+            ahead=result.ahead,
+            behind=result.behind,
+        )
+    except RuntimeError as e:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(e))
+
+
+async def create_branch_with_validation(
+    session: AsyncSession,
+    project_id: uuid.UUID,
+    repo_id: uuid.UUID,
+    data: BranchCreateRequest,
+) -> dict:
+    repo = await get_repo_and_validate(session, repo_id, project_id)
+    ensure_repo_on_disk(repo)
+    try:
+        create_branch(repo.path, data.name, data.base_branch)
+        return {"message": f"Branch '{data.name}' created", "branch": data.name}
+    except RuntimeError as e:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(e))
+
+
+async def delete_branch_with_validation(
+    session: AsyncSession,
+    project_id: uuid.UUID,
+    repo_id: uuid.UUID,
+    branch_name: str,
+    force: bool = False,
+) -> dict:
+    repo = await get_repo_and_validate(session, repo_id, project_id)
+    ensure_repo_on_disk(repo)
+    try:
+        delete_branch(repo.path, branch_name, force)
+        return {"message": f"Branch '{branch_name}' deleted"}
+    except RuntimeError as e:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(e))
+
+
+async def checkout_branch_with_validation(
+    session: AsyncSession,
+    project_id: uuid.UUID,
+    repo_id: uuid.UUID,
+    data: CheckoutRequest,
+) -> dict:
+    repo = await get_repo_and_validate(session, repo_id, project_id)
+    ensure_repo_on_disk(repo)
+    try:
+        checkout_branch(repo.path, data.branch)
+        return {"message": f"Checked out branch '{data.branch}'", "branch": data.branch}
+    except RuntimeError as e:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(e))
+
+
+async def commit_changes_with_validation(
+    session: AsyncSession,
+    project_id: uuid.UUID,
+    repo_id: uuid.UUID,
+    data: CommitRequest,
+    user: User,
+) -> dict:
+    repo = await get_repo_and_validate(session, repo_id, project_id)
+    ensure_repo_on_disk(repo)
+    author_name = user.name or "Unknown"
+    author_email = user.email or "unknown@example.com"
+    try:
+        commit_hash = commit_changes(
+            repo_path=repo.path,
+            message=data.message,
+            author_name=author_name,
+            author_email=author_email,
+            files=data.files,
+        )
+        return {"commit_hash": commit_hash, "message": data.message}
+    except RuntimeError as e:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(e))
+
+
+async def fetch_with_validation(
+    session: AsyncSession,
+    project_id: uuid.UUID,
+    repo_id: uuid.UUID,
+) -> FetchResponse:
+    repo = await get_repo_and_validate(session, repo_id, project_id)
+    ensure_repo_on_disk(repo)
+    try:
+        fetch(repo.path)
+        return FetchResponse(message="Fetched from remote")
+    except RuntimeError as e:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(e))
+
+
+async def pull_with_validation(
+    session: AsyncSession,
+    project_id: uuid.UUID,
+    repo_id: uuid.UUID,
+    branch: str | None = None,
+) -> PullResponse:
+    repo = await get_repo_and_validate(session, repo_id, project_id)
+    ensure_repo_on_disk(repo)
+    try:
+        pull(repo.path, branch)
+        return PullResponse(message="Pulled from remote")
+    except RuntimeError as e:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(e))
+
+
+async def push_with_validation(
+    session: AsyncSession,
+    project_id: uuid.UUID,
+    repo_id: uuid.UUID,
+    branch: str | None = None,
+) -> PushResponse:
+    repo = await get_repo_and_validate(session, repo_id, project_id)
+    ensure_repo_on_disk(repo)
+    try:
+        push(repo.path, branch)
+        return PushResponse(message="Pushed to remote")
+    except RuntimeError as e:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(e))
+
+
+async def merge_with_validation(
+    session: AsyncSession,
+    project_id: uuid.UUID,
+    repo_id: uuid.UUID,
+    data: MergeRequest,
+) -> MergeResponse:
+    repo = await get_repo_and_validate(session, repo_id, project_id)
+    ensure_repo_on_disk(repo)
+    try:
+        commit_hash = merge(
+            repo_path=repo.path,
+            source_branch=data.source_branch,
+            target_branch=data.target_branch,
+            message=data.message,
+        )
+        return MergeResponse(
+            commit_hash=commit_hash,
+            message=data.message or f"Merge {data.source_branch}",
+        )
+    except RuntimeError as e:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(e))