Add FastAPI backend and React frontend subprojects

Backend:
- FastAPI app with 17 REST endpoints covering dashboard, monitoring,
  media index, file browser, and jobs
- Reuses existing clients/domain/services unchanged
- pydantic-settings config, dependency injection, CORS setup
- Auto-generated OpenAPI docs at /docs

Frontend:
- Vite + React + TypeScript SPA
- @tanstack/react-query for data fetching with polling
- ag-grid-react for media table and file browser
- recharts for monitoring charts
- Tailwind CSS styling
- 4 pages: Dashboard, Monitoring, Media, File Browser
- Typed API client matching all backend endpoints

Also:
- docs/MIGRATION_PLAN.md with full architecture plan
- Updated .gitignore for both subprojects
- Streamlit app preserved for now (can coexist)

backend/routers/jobs.py

@@ -0,0 +1,51 @@
+"""Jobs router — list templates and run jobs."""
+
+from __future__ import annotations
+
+from typing import Any
+
+from fastapi import APIRouter, Depends, HTTPException
+from pydantic import BaseModel
+
+from dependencies import get_ssh_client
+from clients.ssh import RemoteSSHClient
+from jobs import JOB_TEMPLATES, run_job
+
+router = APIRouter(prefix="/api/jobs", tags=["jobs"])
+
+
+class RunJobRequest(BaseModel):
+    job_key: str
+    path: str
+
+
+@router.get("/templates")
+def get_templates() -> list[dict[str, str]]:
+    """Return available job templates."""
+    return [
+        {
+            "key": key,
+            "name": template.name,
+            "description": template.description,
+        }
+        for key, template in JOB_TEMPLATES.items()
+    ]
+
+
+@router.post("/run")
+def post_run_job(
+    request: RunJobRequest,
+    ssh: RemoteSSHClient = Depends(get_ssh_client),
+) -> dict[str, Any]:
+    """Run a job template on a remote path."""
+    if request.job_key not in JOB_TEMPLATES:
+        raise HTTPException(status_code=400, detail=f"Unknown job key: {request.job_key}")
+
+    result = run_job(ssh, request.job_key, request.path)
+    return {
+        "job_key": request.job_key,
+        "path": request.path,
+        "exit_status": result.exit_status,
+        "stdout": result.stdout,
+        "stderr": result.stderr,
+    }