Implement M1 authoring loop: library, editor, live preview, persistence

M1 MVP from docs/IMPLEMENTATION-PLAN.md, with the /alignment pass applied.

- core: Snippet model + factory; prepareSpecForRender (copy-not-mutate); per-theme Vega chart config
- state/orchestration: SnippetStore with debounced auto-save; IndexedDB adapter + read-time migration; startup hydration + write-through persistence
- ui: SnippetLibrary, SpecEditor (Monaco edcore.main — full editor features, JSON-only languages), LivePreview
- build: Monaco/Vega manual chunks; raised PWA precache ceiling
- alignment: flush a valid draft on snippet switch (+regression tests); TODO breadcrumbs for the preview render race and the window.confirm delete
- housekeeping: gitignore .claude/projects/

AGENTS.md

@@ -79,7 +79,16 @@ npm run format     # Prettier
 ### AI Developer Protocol
 
 - **No git on your own initiative** — don't `add`/`commit`/`push` unless explicitly invited.
-- **Verify** — run `npm run typecheck` and `npm test` after changes.
+- **Verify** — run `npm run typecheck` and `npm test` after changes. A green build and a
+  smaller bundle prove nothing about behavior: when a change touches what the user sees or
+  does, confirm it by exercising the feature, not by the compiler alone.
+- **Trim content, not capability** — when narrowing a third-party import or build to cut
+  size, remove optional _content_ (languages, locales, themes, icon sets), never the
+  library's _features_. The smallest/lowest-level entry point is seldom the right one — it
+  often drops capabilities you meant to keep. Prefer the entry that excludes the unwanted
+  content while retaining behavior, and validate the behavior survived. (This bit us once:
+  importing Monaco's `editor.api` to drop unused languages also stripped every editor
+  feature — see `docs/architecture/08`.)
 - **Spec is the contract** — when in doubt, read `docs/spec/`. If the spec is wrong or
   silent, raise it; change the spec deliberately rather than drifting from it.
 - **Core-first** — for each feature, build the pure `src/core/` logic with tests before UI.