chore(agents): replace Cursor rule with tool-agnostic skill

- Preserve shipped-data tracking and validation guidance
- Move repository instructions into the shared agent skill format

.agents/skills/shipped-data-assets/SKILL.md

@@ -0,0 +1,29 @@
+---
+name: shipped-data-assets
+description: Keep shipped data assets present in git branch archives and tool updates. Use when adding or changing defaults under data/, editing their .gitignore rules, changing the update installer, or updating bundled-data coverage in tests/test_bundled_updates.py.
+---
+
+# Shipped Data Assets
+
+Tool auto-update downloads a git branch archive. Files matched by `.gitignore` are omitted from that archive and never reach users.
+
+## Maintain shipped defaults
+
+- Add a `.gitignore` negation for every shipped path under `data/`, following existing patterns such as:
+  - `!data/skills/**`
+  - `!data/help/**`
+  - `!data/vocab_base.txt`
+  - `!data/translation_contexts.json`
+- Do not rely on `UpdateThread.should_install` alone; ignored files never appear in the downloaded archive.
+- Extend `_SHIPPED_DATA_FILES` or `ShippedDataTrackingTests` in `tests/test_bundled_updates.py` when adding a shipped path.
+- Keep user-local files ignored and protected, including `data/vocab.txt`, `data/last_update_sha.txt`, `data/wolf_*.json`, and `data/api_keys.json`.
+
+## Verify tracking
+
+Run `git check-ignore -- <shipped-path>` for each affected file. A shipped path must exit with status 1, indicating that it is not ignored.
+
+Run the bundled-update tests after changing shipped paths, ignore rules, or installer behavior:
+
+```bash
+python -m unittest tests.test_bundled_updates.ShippedDataTrackingTests
+```

.cursor/rules/shipped-data-assets.mdc

@@ -1,27 +0,0 @@
----
-description: Shipped data/ assets must be git-trackable so tool updates include them
-globs: "{.gitignore,data/**,gui/guide_tab.py,gui/main.py,tests/test_bundled_updates.py}"
-alwaysApply: false
----
-
-# Shipped data/ and tool updates
-
-Tool auto-update downloads a **git branch archive**.
-Anything matched by `.gitignore` is omitted from that archive and never reaches users.
-
-## When adding or changing shipped defaults under `data/`
-
-- Add a negation under `.gitignore` (same pattern as skills/help):
-  - `!data/skills/**`
-  - `!data/help/**`
-  - `!data/vocab_base.txt`
-  - `!data/translation_contexts.json`
-- Do **not** rely on `UpdateThread.should_install` alone - ignored files never appear in the zip.
-- Extend `_SHIPPED_DATA_FILES` / `ShippedDataTrackingTests` in `tests/test_bundled_updates.py` when adding a new shipped path.
-- User-local files stay ignored/protected: `data/vocab.txt`, `data/last_update_sha.txt`, `data/wolf_*.json`, `data/api_keys.json`.
-
-## Quick check
-
-```bash
-git check-ignore -- data/help/index.json   # must exit 1 (not ignored)
-```