Add isolated worktree development environments - #1

Talebound's previous local setup shared fixed ports and required manual environment configuration. This adds a repeatable Linux/WSL setup so multiple worktrees can run independently, including their database, background email jobs, and browser sessions.

Changes

• Add an agent-neutral bootstrap and setup, up, status, logs, restart, migrate, test-backend, and down commands using Docker Compose and Python's standard library.
• Give each worktree its own PostgreSQL database, Redis queue, Mailpit inbox, loopback address, ports, and generated credentials. Keep runtime configuration ignored by Git and use host-only cookies to isolate sessions.
• Preserve data on normal stops; require matching ownership labels before cleanup. Add concurrent-worktree lifecycle tests and a GitHub Actions workflow.
• Honor SMTP_ENDPOINT so local signup and password-reset emails arrive in Mailpit without AWS credentials. Add a local SMTP delivery test; the existing deployed configuration continues to specify SES.
• Add Suspense boundaries around the authenticated header and image-backed avatars to prevent blank pages after login or avatar changes.
• Restore passing frontend checks: remove unused legacy code, deduplicate React types, replace the ambient Redux override with typed hooks, and align image/location consumers and cache updates with the generated API.
• Update AGENTS.md, the root Makefile, and the development guides with bootstrap, environment, validation, and cleanup instructions.

Validation

• Bootstrapped and ran two complete worktree instances simultaneously; verified separate databases, queues, inboxes, addresses, credentials, and browser sessions.

• Concurrent lifecycle integration test passed: repeated setup, stop/restart persistence, foreign-resource refusal, and purging one stack while the other remains usable.

• Backend short test suite passed against the migrated worktree database, including the new SMTP test.

• Browser checks passed for signup, verification email delivery, email verification, login, Worlds/Systems/Characters/Quests, password reset, and login with the changed password. Backend restart and subsequent login also passed.

• Bash/Python syntax checks, workflow actionlint, Makefile command checks, and git diff --check passed.

• Locked Yarn installation, full frontend ESLint, TypeScript checking, and the Next.js production build passed under Node 22. Lint and type checking remain enabled.

• Browser regressions passed for paginated location loading, edit, bulk deletion, creation, and map/post lists. Image-list invalidation after upload, avatar upload, and profile rendering passed with mocked image responses; real Cloudflare upload was not exercised.