admin/system: move status panel above tabs, add collapse toggle

Status (services, PHP env, disk) is now always visible above the log/config
tab bar rather than being one of the tab targets:

- Status section rendered unconditionally above <nav class="sys-tabs">.
- Services grid, PHP info grid and disk bar grouped inside a collapsible
  <section> with a header row containing the cache-freshness badge and a
  toggle button (▲ Réduire / ▼ Développer).
- Collapse state persisted in localStorage so the preference survives
  page reloads (e.g. when switching log tabs).
- Tab bar now only contains the three log tabs + nginx config; the 'Statut'
  tab is removed. Legacy ?tab=status URLs fall through to nginx_access.
- PHP/disk sub-sections laid out in a 2-col grid inside the status panel;
  responsive single-col below 700px.
- system.css: new .sys-status-section / .sys-status-header /
  .sys-status-toggle / .sys-status-meta rules added.
- aria-current="page" added to active tab links.
- todo/03-system-cache.md: all items marked done; notes added explaining
  why log caching was deliberately omitted.

todo/03-system-cache.md

@@ -1,4 +1,4 @@
-# System Page Caching — Database-Backed Status Cache
+# System Page Caching - Database-Backed Status Cache
 
 ## Problem
 
@@ -11,17 +11,23 @@ The admin system page (`/admin/system.php`) runs expensive operations on every l
 
 ## Solution: `system_cache` table + background refresh
 
-- [ ] **Add `system_cache` table** to schema: `CREATE TABLE system_cache (key TEXT PRIMARY KEY, value TEXT NOT NULL, updated_at INTEGER NOT NULL)`
-- [ ] **Add migration** `storage/migrations/007_system_cache.sql`
-- [ ] **Add `SystemCache` class** (`src/SystemCache.php`) with methods:
+- [x] **Add `system_cache` table** to schema: `CREATE TABLE system_cache (key TEXT PRIMARY KEY, value TEXT NOT NULL, updated_at INTEGER NOT NULL)`
+- [x] **Add migration** `storage/migrations/007_system_cache.sql`
+- [x] **Add `SystemCache` class** (`src/SystemCache.php`) with methods:
   - `get(string $key, int $maxAgeSec = 60): ?array`
   - `set(string $key, array $data): void`
   - `isStale(string $key, int $maxAgeSec = 60): bool`
-- [ ] **Refactor `system.php` status section**:
+- [x] **Refactor `system.php` status section**:
   1. Check `SystemCache::get('system_status', 120)` — 2-minute TTL
-  2. If cache hit → render from cache, show "mis en cache il y a X sec" label
+  2. If cache hit → render from cache, show “mis en cache il y a X sec” label
   3. If cache miss → run checks, store in cache, render
   4. Add `?refresh=1` GET param to force-bypass cache
-- [ ] **Refactor `system.php` log sections** — avoid re-reading on every tab switch; only read the active tab's log
-- [ ] **Cache disk info** separately with 5-minute TTL: `SystemCache::get('disk_info', 300)`
-- [ ] **Cache PHP info** separately with 1-hour TTL: `SystemCache::get('php_info', 3600)`
+- [x] **Refactor `system.php` log sections** — avoid re-reading on every tab switch; only read the active tab’s log
+- [x] **Cache disk info** separately with 5-minute TTL: `SystemCache::get('disk_info', 300)`
+- [x] **Cache PHP info** separately with 1-hour TTL: `SystemCache::get('php_info', 3600)`
+
+## Notes
+
+- Log caching deliberately omitted: `tail` output is inherently real-time and caching even 30s would show stale data during the moments it matters most (deploys, errors). The existing tab guard already ensures only the active log file is read.
+- nginx config could be cached but `file()` on a small static config file is negligible; not worth the added complexity.
+- A future improvement could stream log tabs via `fetch()` to avoid full-page reloads on tab switch.