Restore TODO.md and move TODO content out of README (#58)

Reviewed-on: #58
Co-authored-by: sneak <sneak@sneak.berlin>
Co-committed-by: sneak <sneak@sneak.berlin>

README.md

@@ -893,95 +893,7 @@ linted, tested, and compiled.
 
 ## TODO
 
-### Completed: Code Quality (Phase 1 of MVP)
-- [x] Rename Processor → Webhook, Webhook → Entrypoint in code
-      ([#12](https://git.eeqj.de/sneak/webhooker/issues/12))
-- [x] Embed templates via `//go:embed`
-      ([#7](https://git.eeqj.de/sneak/webhooker/issues/7))
-- [x] Use `slog.LevelVar` for dynamic log level switching
-      ([#8](https://git.eeqj.de/sneak/webhooker/issues/8))
-- [x] Simplify configuration to prefer environment variables
-      ([#10](https://git.eeqj.de/sneak/webhooker/issues/10))
-- [x] Remove redundant `godotenv/autoload` import
-      ([#11](https://git.eeqj.de/sneak/webhooker/issues/11))
-- [x] Implement authentication middleware for protected routes
-      ([#9](https://git.eeqj.de/sneak/webhooker/issues/9))
-- [x] Replace Bootstrap with Tailwind CSS + Alpine.js
-      ([#4](https://git.eeqj.de/sneak/webhooker/issues/4))
-
-### Completed: Core Webhook Engine (Phase 2 of MVP)
-- [x] Implement webhook reception and event storage at `/webhook/{uuid}`
-- [x] Build event processing and target delivery engine
-- [x] Implement HTTP target type (fire-and-forget with max_retries=0,
-      retries with exponential backoff when max_retries>0)
-- [x] Implement database target type (store events in per-webhook DB)
-- [x] Implement log target type (console output)
-- [x] Implement Slack target type (Slack/Mattermost incoming webhook
-      notifications with pretty-printed payloads)
-- [x] Webhook management pages (list, create, edit, delete)
-- [x] Webhook request log viewer with pagination
-- [x] Entrypoint and target management UI
-
-### Completed: Per-Webhook Event Databases
-- [x] Split into main application DB + per-webhook event DBs
-- [x] Per-webhook database lifecycle management (create on webhook
-      creation, delete on webhook removal)
-- [x] `WebhookDBManager` component with lazy connection pooling
-- [x] Event-driven delivery engine (channel notifications + timer-based retries)
-- [x] Self-contained delivery tasks: in the ≤16KB happy path, the engine
-      delivers without reading from any database — target config, event
-      headers, and body are all carried inline in the channel notification.
-      The engine only touches the DB to record results (success/failure).
-      Large bodies (≥16KB) are fetched from the per-webhook DB on demand.
-- [x] Database target type marks delivery as immediately successful
-      (events are already in the per-webhook DB)
-- [x] Parallel fan-out: all targets for an event are delivered via
-      the bounded worker pool (no goroutine-per-target)
-- [x] Circuit breaker for HTTP targets with retries: tracks consecutive
-      failures per target, opens after 5 failures (30s cooldown),
-      half-open probe to test recovery
-
-### Completed: Security Hardening
-- [x] Security headers middleware (HSTS, CSP, X-Frame-Options,
-      X-Content-Type-Options, Referrer-Policy, Permissions-Policy)
-      ([#34](https://git.eeqj.de/sneak/webhooker/issues/34))
-- [x] Session regeneration on login to prevent session fixation
-      ([#38](https://git.eeqj.de/sneak/webhooker/issues/38))
-- [x] Request body size limits on form endpoints
-      ([#39](https://git.eeqj.de/sneak/webhooker/issues/39))
-
-### Remaining: Core Features
-- [ ] Per-webhook rate limiting in the receiver handler
-- [ ] Webhook signature verification (GitHub, Stripe formats)
-- [x] CSRF protection for forms
-      ([#35](https://git.eeqj.de/sneak/webhooker/issues/35))
-- [x] SSRF prevention for HTTP delivery targets
-      ([#36](https://git.eeqj.de/sneak/webhooker/issues/36))
-- [x] Login rate limiting (per-IP brute-force protection)
-      ([#37](https://git.eeqj.de/sneak/webhooker/issues/37))
-- [ ] Session expiration and "remember me"
-- [ ] Password change/reset flow
-- [ ] API key authentication for programmatic access
-- [ ] Manual event redelivery
-- [ ] Analytics dashboard (success rates, response times)
-- [ ] Delivery status and retry management UI
-
-### Remaining: Event Maintenance
-- [ ] Automatic event retention cleanup based on `retention_days`
-
-### Remaining: REST API
-- [ ] RESTful CRUD for webhooks, entrypoints, targets
-- [ ] Event viewing and filtering endpoints
-- [ ] Event redelivery endpoint
-- [ ] OpenAPI specification
-
-### Future
-- [ ] Email delivery target type
-- [ ] SNS, S3, Slack delivery targets
-- [ ] Data transformations (e.g., webhook-to-Slack message formatting)
-- [ ] JSONL file delivery with periodic S3 upload
-- [ ] Webhook event search and filtering
-- [ ] Multi-user with role-based access
+See [TODO.md](TODO.md).
 
 ## License