Initial scaffold: tooling, plan, task briefs

- pnpm 10 workspace + TypeScript strict + ESLint flat + Prettier
- CLAUDE.md as canonical brief
- docs/tasks/ — 22 task briefs broken out by phase for sub-sessions
- docs/decisions/ — ADR scaffold

Implements task 01 (repo-init).

docs/tasks/04-module-loader.md

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+# 04 — Module loader & registry
+
+## Goal
+
+Implement the module system that everything else hangs off: each module declares a manifest, the loader composes them at startup, and core services iterate the registry instead of hardcoding entity types.
+
+## Why
+
+This is the load-bearing extensibility piece. Get this wrong and every later module needs core changes.
+
+## Depends on
+
+- 03 (DB)
+
+## Scope
+
+### Module manifest type (`src/modules/_core/module.ts`)
+
+```ts
+export type ModuleManifest = {
+  id: string; // "calendar", "lists", "notes"
+  name: string; // human-readable
+  nav?: { href: string; label: string; icon?: string };
+  entities: EntityTypeRegistration[]; // see below
+  dashboardWidgets?: DashboardWidget[];
+  quickAdds?: QuickAddAction[];
+};
+
+export type EntityTypeRegistration = {
+  type: string; // "calendar.event", "lists.item", "notes.note"
+  label: { singular: string; plural: string };
+  share?: ShareCapabilities; // null = not shareable
+  reminder?: ReminderCapabilities; // null = not remindable
+  search?: SearchAdapter; // null = not searchable
+  resolveUrl: (id: string) => string; // canonical app URL
+  loadForShare?: (id: string) => Promise<unknown>; // payload for /s/<token>
+};
+```
+
+### Registry (`src/modules/_core/registry.ts`)
+
+- `registerModule(manifest)` and `getRegistry()` returning frozen views.
+- `getEntityType(type)` lookup.
+- Import-time side-effect free: modules are listed and registered explicitly in `src/modules/index.ts`.
+
+### Loader (`src/modules/index.ts`)
+
+- Imports each module's manifest and calls `registerModule`. Order is deterministic.
+- Stub modules for now: `calendar`, `lists`, `notes` each export an empty-but-valid manifest so the loader has something to register.
+
+### Wiring
+
+- Root layout reads the registry to render nav.
+- A throwaway `/debug/registry` page (dev-only) dumps the loaded registry as JSON.
+
+## Out of scope
+
+- Real implementations of share / reminder / search adapters (later phases).
+- Dynamic plugin loading from disk. Modules are statically imported.
+
+## Acceptance criteria
+
+- [ ] `src/modules/index.ts` registers three stub modules.
+- [ ] Nav renders entries from the registry, not from a hardcoded list.
+- [ ] `/debug/registry` shows all three module manifests in dev.
+- [ ] Adding a fourth stub module only requires creating its folder + adding one line to `src/modules/index.ts`.
+- [ ] All types exported from `_core` so other modules can import without circulars.
+
+## Notes
+
+- Frozen objects (`Object.freeze`) on registry exposure are cheap insurance against accidental mutation.
+- Resist the urge to make this a fancy DI container. A plain map is enough.