## Summary
Switches tessl from **vendored** mode to **managed** mode
([docs](https://docs.tessl.io/reference/configuration#project-mode-managed-vs-vendored)).
Previously, all tile contents (~170k lines across 449 files) were
committed directly in `.tessl/tiles/`. This bloated the repo and added
noise to diffs/context that the team found hard to review.
In managed mode, tiles work like `node_modules` — they're gitignored and
fetched from the registry on demand.
## What changed
- `tessl.json`: `"mode": "vendored"` → `"mode": "managed"`
- `.gitignore`: added `.tessl/tiles/`
- Removed all files under `.tessl/tiles/` from git tracking (they remain
on disk locally)
## After merging
Team members need to run **`tessl install`** once after pulling this
change to restore their local tiles. This is the same workflow as
running `npm install` after dependency changes.
## Test plan
- [x] `tessl install` restores all tiles locally after the change
- [ ] Verify CI/remote agents still work (they'll need `tessl install`
in their setup step if they use tiles)
