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)

docs/REQUIREMENTS.md

@@ -8,7 +8,7 @@ Build a compact Streamlit application for browsing a remote Jellyfin media libra
 
 ## Current Phase
 
-Phase 1: Jellyfin library browser plus SSH-based remote filesystem inspection and safe job templates.
+Phase 1: Jellyfin media index, SSH-based remote filesystem inspection, server monitoring, and safe job templates.
 
 ## Core Requirements
 
@@ -91,14 +91,15 @@ Phase 1: Jellyfin library browser plus SSH-based remote filesystem inspection an
 - Keep a manual `ffprobe` action available for selected paths.
 - Support `stat` on selected paths.
 
-### Dashboard / Server Resources
+### Dashboard / Server Monitoring
 
 - Provide a dashboard tab with a compact Jellyfin media library overview and server resource overview.
 - Show Jellyfin media counts for movies, series, and series episodes on the dashboard.
 - Show currently playing Jellyfin sessions on the dashboard, including user, media title, playback state, and whether transcoding is active.
 - Provide a dashboard tab with a compact server resource overview over SSH.
-- Provide a separate Resources tab for detailed resource charts, collector controls, diagnostics, and raw samples.
+- Provide a separate Monitoring tab for detailed resource charts, collector controls, diagnostics, and raw samples.
 - Show CPU and RAM usage for the last hour.
+- Show IO wait percentage for the last hour.
 - Show average and spike/peak values for network throughput and disk I/O.
 - Show used, available, and total disk space for the configured media root, falling back to `/`.
 - Use a lightweight remote collector that reads Linux `/proc`, `/sys/block`, and `df` data into a JSONL file under `/tmp`.
@@ -274,8 +275,8 @@ Local app dependencies are declared in `pyproject.toml`; `requirements.txt` inst
 - Changed network display units from bits per second to bytes per second to avoid Kbps/KB/s ambiguity; the collector still stores bit-rate compatibility fields for old/debug consumers.
 - Scaled network and disk throughput charts into readable units such as KB/s, MB/s, and GB/s instead of plotting raw base units.
 - Updated collector startup to remove old temporary metrics/log files when a new collector process is started after a schema/display change.
-- Moved detailed resource charts, raw samples, diagnostics, and collector controls into a dedicated Resources tab; the Dashboard now keeps a compact overview.
-- Removed the CPU/RAM chart from the Dashboard and kept detailed charts in the Resources tab.
+- Moved detailed resource charts, raw samples, diagnostics, and collector controls into a dedicated Monitoring tab; the Dashboard now keeps a compact overview.
+- Removed the CPU/RAM chart from the Dashboard and kept detailed charts in the Monitoring tab.
 - Renamed the remote files tab to File browser.
 - Added Jellyfin media counts for movies, series, and episodes to the Dashboard using lightweight count queries.
 - Added a Dashboard now-playing section sourced from Jellyfin sessions, showing who is currently playing what and whether each session is transcoding.
@@ -297,6 +298,9 @@ Local app dependencies are declared in `pyproject.toml`; `requirements.txt` inst
 - Restored File browser table row selection with AG Grid (single-select), using a table interaction style consistent with the Media tab.
 - Reintroduced open-on-select behavior in File browser: selecting a directory row (including `[UP] ..`) opens it immediately, while file rows update selected target path.
 - Refined Media table column presentation with explicit user-friendly headers and null-safe display formatting to keep the grid readable and consistent.
+- Renamed Resources tab to Monitoring; added IO wait (iowait) percentage to the collector script, metrics, dashboard summary, and detailed charts.
+- Removed the Jellyfin library poster-grid tab and its associated cached API calls and UI module; the Media index tab now covers library browsing needs.
+- Simplified File browser navigation: removed Up/Go/Select folder buttons; pressing Enter in the path text input navigates directly.
 - Added broad inline/module documentation across clients, domain, services, and Streamlit adapter modules to make debugging and future frontend extraction easier.
 - Simplified the File browser by removing its interactive AG Grid and using a read-only listing with explicit Open/Select controls, reducing cross-tab state interactions with the Media grid.
 - Removed optional/compatibility code paths around the Media table grid and old file-browser state aliases to keep the interaction model easier to reason about during debugging.