Add Docker support and refactor prompt/queue internals

- Add Dockerfile, docker-compose.yml, .dockerignore for containerised deployment
- Extract _resolve_character(), _ensure_character_fields(), _append_background() helpers to eliminate repeated inline character-field injection and background-tag patterns across all secondary-category generate routes
- Add _IDENTITY_KEYS / _WARDROBE_KEYS constants
- Fix build_extras_prompt() bug: detailer prompt (a list) was being appended as a single item instead of extended
- Replace all per-route _finalize closures with _make_finalize() factory, reducing duplication across 10 generate routes
- Add _prune_job_history() called each worker loop iteration to prevent unbounded memory growth
- Remove 10 orphaned legacy finalize_generation HTTP routes and check_status route (superseded by job queue API since job-queue branch)
- Remove one-time migration scripts (migrate_actions, migrate_detailers, migrate_lora_weight_range, migrate_wardrobe)
- Update CLAUDE.md and README.md to document new helpers, queue architecture, and Docker deployment

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,8 @@
+venv/
+__pycache__/
+*.pyc
+instance/
+flask_session/
+static/uploads/
+tools/
+.git/