feat(content): add places, code mode, mobile context tab, and detail views

- Add Places/Restaurants content type with PlaceCard, PlaceDetail, PlaceGrid
- Add WebsiteDetail and MagazineSectionDetail views for Context panel
- Enhance MagazineGrid hero with background image and 3x taller header
- Add mobile 3-tab layout (Chat, Content, Context) with detail navigation
- Add /code command system: useCodeContext composable, ProjectGrid, FileTreeNode,
  CodeDetail for IDE-style code viewing across all three panels
- Fix /code bubble and prompt index clicks to re-activate code mode
- Fix updatePanelFromText overwriting code tab by skipping command messages

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/app/src/composables/useAI.ts

@@ -43,6 +43,8 @@ Prioritize Podcasting 2.0–friendly platforms: Fountain.fm, Podcast Index, Cast
 
 **TV Series:** When recommending or discussing TV series/shows, use [[tv_ext:Title|Year|Creator]], e.g. [[tv_ext:Breaking Bad|2008|Vince Gilligan]]. Do NOT use [[film_ext:...]] for TV series — use [[tv_ext:...]] instead. Write a brief reason why the show is worth watching on the same line.
 
+**Places/Restaurants:** When recommending restaurants, cafes, bars, or other places to visit, use [[place_ext:Name|Cuisine|City|Rating|PriceLevel|Address]], e.g. [[place_ext:Sushi Nakazawa|Japanese|New York|4.7|3|23 Commerce St]]. Rating is out of 5, PriceLevel is 1-4 ($ to $$$$). Omit fields you don't know. Write a brief description on the same line.
+
 **Websites / "Best places to check":** When listing resources, places to check online, or websites for the user to visit, use markdown links: [Name](https://full-url). For simple domains use **Name** (domain.com), e.g. **Bitcoin Mailing List** (gnusha.org).
 
 **Music discovery:** For genre-based requests (e.g. "best math rock"), pick from the user's library when relevant, or use [[song_ext:...]] for others. Prioritize indie-friendly platforms: Wavlake, Bandcamp, Internet Archive, SoundCloud, Odysee, Jamendo.