chore: switch texthooker-ui workflow to pnpm and add backlog tasks

backlog/tasks/task-78 - Modularize-config-definitions-and-validation-by-domain.md

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+---
+id: TASK-78
+title: Modularize config definitions and validation by domain
+status: To Do
+assignee: []
+created_date: '2026-02-18 11:43'
+updated_date: '2026-02-18 11:43'
+labels:
+  - config
+  - refactor
+  - maintainability
+dependencies:
+  - TASK-69
+  - TASK-72
+priority: high
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Config defaults and resolution are still concentrated in large files (`src/config/definitions.ts`, `src/config/service.ts`). This task splits config schema/defaults/validation into domain modules while preserving a single composed public config API.
+<!-- SECTION:DESCRIPTION:END -->
+
+## Suggestions
+
+<!-- SECTION:SUGGESTIONS:BEGIN -->
+- Organize by domain (`anki`, `subtitle`, `jellyfin`, `anilist`, `launcher`, `runtime`).
+- Keep one composition root that merges domain validators and defaults.
+- Prefer small reusable validator helpers over per-field inline logic.
+<!-- SECTION:SUGGESTIONS:END -->
+
+## Action Steps
+
+<!-- SECTION:PLAN:BEGIN -->
+1. Define domain module boundaries for defaults + validation rules.
+2. Extract domain validators with shared primitives and warning builder.
+3. Compose resolved config in a central aggregator module.
+4. Keep `ConfigService` external API stable.
+5. Expand tests for domain-level validation and composed config output.
+6. Update config docs to reflect module ownership and extension workflow.
+<!-- SECTION:PLAN:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [ ] #1 Config definitions/validation are split by domain with clear ownership
+- [ ] #2 `ConfigService` API remains backward-compatible
+- [ ] #3 Validation behavior remains stable under existing tests
+- [ ] #4 New domain-level tests prevent regression in future config additions
+<!-- AC:END -->
+
+## Definition of Done
+<!-- DOD:BEGIN -->
+- [ ] #1 Config and core tests pass
+- [ ] #2 Documentation updated for config extension workflow
+<!-- DOD:END -->
+