Implement the following plan:

# Plan: Video Studio UX Overhaul — Filmstrip UI + Real-Time Feedback + Parallel Generation

## Context

The video studio has minimal feedback during generation. After clicking "generate", users see a progress ring and "scene X of Y". Images are generated but never shown. Scenes can't be expanded. No receipt/project ID is shown. Generation is sequential (slow). This plan fixes all of that.

## Urgent Pre-requisite

- Add `XAI_API_KEY` to systemd service so Grok video gen works
- Add a "resume" endpoint to retry video gen from the images step for the failed project `af830b6b`

## Files to Modify

### 1. `templates/video.html` — UI overhaul

**New layout changes:**
- **Receipt**: After POST returns, show project ID (`af830b6b`) prominently + auto-add to left panel project list
- **Filmstrip**: Below the video viewport — horizontal scrolling strip of scene frames (120px wide, 16:9 ratio, film sprocket aesthetic). Each frame:
  - Initially: dark placeholder with scene number
  - After image gen: shows actual image (`/data/images/video_XXXX_NN.png`)
  - After video gen: green border
  - Click: opens detail overlay (image full-size, image_prompt, video_prompt, narration, duration, status)
- **Progress label**: Shows current step ("generating images 3/14...", "generating videos 5/14...", "stitching...")
- **Remove**: progress ring overlay → replace with filmstrip + step label in-place
- **Script panel (right)**: Keep but make each scene card expandable (click to toggle full prompts/narration)
- **Past projects**: Show project short-ID as receipt code

**Polling enhancement (JS):**
- Existing 3s poll already returns `script.scenes` with per-scene status + `image_url`
- Update filmstrip frames when `image_path` appears on a scene
- Show `current_step` from API response
- Auto-scroll filmstrip to the active scene

### 2. `src/pipeline/video_gen.rs` — Parallel generation

**`generate_scene_images`**: Replace sequential loop with `tokio::JoinSet` + `Arc<Semaphore>` (3 concurrent). After each image completes, update DB `script_json` so poll endpoint picks it up immediately.

**`generate_scene_videos`**: Submit up to 3 Grok jobs concurrently, poll all active jobs in a unified loop (every 5s). As each completes, download clip. Update DB after each.

**Add `current_step` tracking**: Call new `update_video_project_step()` at each phase transition.

### 3. `src/routes/api.rs` — Enhanced poll + resume

**`get_video_project`**: Add `current_step` to response.

**Add `POST /api/v1/video/{id}/resume`**: Resume a failed video project from where it left off (e.g. images done but videos failed → skip to step 2).

### 4. `src/db/queries.rs` + `src/db/migrations.rs`

- Add `current_step TEXT DEFAULT 'script'` column to `video_projects`
- Add `update_video_project_step(conn, id, step)` function

### 5. `~/.config/systemd/user/anky.service`

- Add `Environment=XAI_API_KEY=...` line

## Verification

1. `cargo build --release`
2. `systemctl --user daemon-reload && systemctl --user restart anky.service`
3. Resume the failed project `af830b6b` (images already generated)
4. New video generation → verify filmstrip shows images, parallel gen works, receipt shown