Update stale README Project Structure tree and migrations docs (#45)

Cross-checking README.md against the actual file tree found three gaps:
views/error_403.php and error_404.php (plus error_500.php, added since
the issue was filed) weren't listed under views/; config/requirements.php
wasn't listed under config/ (confirmed it's not a duplicate of
scripts/check_requirements.php — it's the shared data source both that
script and api/health.php read from); and the Database Schema section
only described 000_baseline.sql and migrate.php generically, with no
mention that four numbered migrations now exist on top of the baseline.

Updated the Project Structure tree and the Database Schema/Migrations
prose to list all of these, noting that 000_baseline.sql already
includes every numbered migration's changes for a fresh install (they
only matter when upgrading an existing database).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lhz7pGMaoTfL5sdYS5XiKv

README.md

@@ -255,6 +255,7 @@ Content-Type: application/json
 
 - `migrations/000_baseline.sql` is the full schema baseline for the whole database. It is written to be safe to re-run (idempotent) and is the source of truth for a fresh install.
 - `php migrations/migrate.php` applies any pending migration files in `migrations/` in order, tracking applied files in the `migrations` table. Use `--status` to list state and `--dry-run` to preview without executing.
+- Numbered migrations on top of the baseline (all idempotent, safe to re-run): `001_widen_bulk_operations_status.sql`, `002_fix_collation_consistency.sql`, `003_fk_on_delete_set_null.sql`, `004_fix_ticket_watchers_type.sql`. A fresh install via `000_baseline.sql` already includes all of these; they only matter for upgrading an existing database.
 
 ### API Endpoints
 
@@ -348,7 +349,9 @@ tinker_tickets/
 │   └── images/
 │       └── favicon.png
 ├── config/
-│   └── config.php                        # Config + .env loading
+│   ├── config.php                        # Config + .env loading
+│   └── requirements.php                  # PHP version/extension requirements (single source of
+│                                          #   truth for scripts/check_requirements.php + api/health.php)
 ├── controllers/
 │   ├── CommentController.php             # Comment create/edit/delete + notifications
 │   ├── DashboardController.php           # Dashboard with stats + filters
@@ -389,6 +392,10 @@ tinker_tickets/
 │   └── WorkflowModel.php                 # Status transition workflows
 ├── migrations/
 │   ├── 000_baseline.sql                  # Full schema baseline (safe to re-run)
+│   ├── 001_widen_bulk_operations_status.sql  # Upgrade-only (already in baseline for fresh installs)
+│   ├── 002_fix_collation_consistency.sql     # Upgrade-only (already in baseline for fresh installs)
+│   ├── 003_fk_on_delete_set_null.sql         # Upgrade-only (already in baseline for fresh installs)
+│   ├── 004_fix_ticket_watchers_type.sql      # Upgrade-only (already in baseline for fresh installs)
 │   └── migrate.php                       # CLI migration runner (tracks applied migrations)
 ├── scripts/
 │   ├── check_requirements.php            # Verify PHP extensions/config prerequisites
@@ -406,6 +413,9 @@ tinker_tickets/
 │   │   └── WorkflowDesignerView.php      # Workflow transition designer
 │   ├── CreateTicketView.php              # Ticket creation with visibility
 │   ├── DashboardView.php                 # Dashboard with kanban + sidebar + charts
+│   ├── error_403.php                     # Access-denied error page
+│   ├── error_404.php                     # Not-found error page
+│   ├── error_500.php                     # Fatal-error page (self-contained, no app-state deps)
 │   ├── layout_footer.php                 # Shared footer (notification polling, boot sequence)
 │   ├── layout_header.php                 # Shared header (nav, command palette, theme toggle)
 │   └── TicketView.php                    # Ticket view with timeline, SLA, watcher avatars