refactor: extract inbox domain and thin ipc handlers

[h4yfans]

What

Reintroduce a narrow @memry/domain-inbox package and move inbox CRUD, batch, and query ownership out of main-process IPC handlers into inbox runtime modules, leaving IPC as a transport layer.

Why

Phase 3 of the architecture reset checklist still described inbox as extracted, but current main had reverted that package and kept persistence/orchestration in inbox-handlers.ts. This restores the intended Phase 3 boundary without claiming the later Phase 4 projection separation work is complete.

How

• restore packages/domain-inbox with pure inbox commands, queries, types, and focused tests
• add apps/desktop/src/main/inbox/domain.ts, crud.ts, batch.ts, and queries.ts to own desktop-side orchestration and adapters
• reduce inbox IPC handler files to thin registration/delegation shells
• wire workspace, Vite, TypeScript, and Vitest config so @memry/domain-inbox resolves correctly
• regenerate the IPC invoke map and update the architecture plan docs

Type

• feat — new feature
• fix — bug fix
• refactor — restructure without behavior change
• style — visual/UI only
• perf — performance improvement
• test — adding or updating tests
• chore — tooling, deps, config
• docs — documentation only
• ci — CI/CD changes

Test plan

• Unit tests added/updated
• Integration tests added/updated
• Manual testing (describe below)

pnpm ipc:check
pnpm --filter @memry/desktop exec vitest run --config config/vitest.config.ts src/main/ipc/inbox-handlers.test.ts
pnpm --filter @memry/desktop exec vitest run --config config/vitest.config.ts src/main/ipc/inbox-query-handlers.test.ts
pnpm --filter @memry/desktop exec vitest run --config config/vitest.config.ts ../../packages/domain-inbox/src/commands.test.ts

Screenshots

N/A

Checklist

• Self-reviewed the diff
• No hardcoded secrets or credentials
• Files stay under ~500 LOC
• Follows immutable data patterns