ui(cards): explicitly signal view level — Episodes vs Scenes mode

[stultus]

Where: `src/lib/components/SceneCardsView.svelte`, `src/lib/components/EpisodeCardsView.svelte`

The core problem: when the writer is in Card View on a series project, there are two distinct levels (Episodes and Scenes). The current chrome doesn't make this difference loud enough — a user who doesn't already know the UI can't immediately tell which level they're looking at.

Looking at the attached screenshot:

• The level indicator is just a small `SERIES · കടൽക്കര / Kadalkara · 5 episodes` strip at the top — eyebrow-style, easy to miss.
• The cards themselves use the same surface, accent, and "Open scenes" button pattern as scene cards.
• The "Cards" tab in the TitleBar reads identically regardless of which level is active.

Suggested fix — multiple compounding signals:

1. Big level title at the top of the cards area. Replace the current eyebrow strip with a real header:
   ```
   EPISODES 5 episodes
   കടൽക്കര / Kadalkara
   ```

   • Eyebrow ("EPISODES" / "SCENES") in 11px caps with letter-spacing — same style as Stats / Export modal eyebrows.
   • Series or episode title underneath, larger / bolder.
   • Right-aligned count badge.

2. Segmented toggle in the toolbar (series only). When in series mode and at the Episode level, show a [Episodes]·[Scenes] segmented control. Click "Scenes" → drills into the active episode. Click the breadcrumb back arrow → returns to Episodes. Two ways into the same state, but the toggle itself communicates that two levels exist.

3. Distinct card surface for episodes vs scenes. Episode cards could use a slightly different geometry — slightly thicker accent edge, gradient header bar, or a printed "EPISODE" tag in the corner — anything that says "this isn't a scene card." Pairs with ui(series): visual rhythm + breathing room — sidebar feels dense #149's broader "rhythm" pass.

4. TitleBar tab label adapts. "Cards" → "Episodes" or "Scenes" depending on the current sub-level (only when in a series). For films, stays "Cards."

The user's main complaint: "it is not very clear, unless the user already knows the UI very well." Pick at least #1 and #2; #3 and #4 are sweeteners.