feat(ui): add usage monitor modal with gauges and model/task usage analysis

Adds a Usage Monitor modal (Worker menu + wired to the footer/Mission-Control
usage pill's Open command): dynamic gauges built from UsageSnapshotDto.Limits
with gate-threshold marks, a stale/blocked-gate band, and Models/Tasks tabs
backed by GetModelUsageAsync/GetTaskUsageAsync over a 7d/30d/custom range.

src/ClaudeDo.Localization/locales/en.json

@@ -422,6 +422,39 @@
       "generate": "Generate",
       "regenerate": "Regenerate",
       "emptyStateHint": "No report for this range yet. Click “Generate”."
+    },
+    "usageMonitor": {
+      "title": "USAGE MONITOR",
+      "windowTitle": "Usage Monitor",
+      "noGauges": "No usage limits reported yet.",
+      "staleFormat": "Values stale (as of {0})",
+      "staleGateHint": "The gate does not apply while values are stale.",
+      "gateBlockedFormat": "Queue paused — {0}",
+      "resetIn": "Reset in {0}",
+      "gaugeSession": "Session (5h)",
+      "gaugeWeeklyAll": "Week (all models)",
+      "gaugeWeeklyScopedFormat": "Week ({0})",
+      "period": "Period:",
+      "last7Days": "7 days",
+      "last30Days": "30 days",
+      "fromDate": "From",
+      "toDate": "To",
+      "modelUsage": "Models",
+      "taskUsage": "Tasks",
+      "emptyStateHint": "No usage data for this range yet.",
+      "columnModel": "MODEL",
+      "columnIn": "IN",
+      "columnOut": "OUT",
+      "columnCache": "CACHE",
+      "columnOtherIn": "OTHER IN",
+      "columnOtherOut": "OTHER OUT",
+      "columnOtherCache": "OTHER CACHE",
+      "columnShare": "SHARE",
+      "columnTask": "TASK",
+      "columnList": "LIST",
+      "columnModelShort": "MODEL",
+      "columnRuns": "RUNS",
+      "columnTotal": "TOTAL"
     }
   },
   "installer": {
@@ -535,6 +568,7 @@
       "restartWorker": "Restart worker",
       "worktrees": "Worktrees…",
       "weeklyReport": "Weekly Report…",
+      "usageMonitor": "Usage Monitor…",
       "about": "About…",
       "addRepos": "Add repos as lists…"
     },
@@ -559,6 +593,7 @@
     "settingsModal": { "workerOffline": "Worker offline — settings read-only.", "saveFailed": "Save failed: {0}" },
     "onlineInbox": { "workerOffline": "Worker offline — cannot load config.", "saved": "Config saved.", "saveFailed": "Save failed: {0}", "signedIn": "Signed in successfully.", "signedInNoRole": "Signed in, but this account is missing the 'user' role in Zitadel — online sync will be rejected until the role is granted in the ClaudeDo project.", "signInFailed": "Sign-in failed: {0}", "signedOut": "Signed out.", "signOutFailed": "Sign-out failed: {0}" },
     "weeklyReport": { "invalidRange": "Invalid date range.", "generating": "Generating report…", "error": "Error: {0}" },
+    "usageMonitor": { "loadFailed": "Couldn't load usage data: {0}" },
     "filesTab": { "workerOffline": "Worker offline.", "noneBundled": "No default agents bundled.", "allPresent": "All default agents already present.", "restored": "Restored {0} default agent(s).", "restoreFailed": "Restore failed: {0}", "openFailed": "Open failed: {0}" },
     "sessionSkillsTab": { "installed": "Installed: {0}", "installFailed": "Install failed: {0}", "updated": "Updated.", "updateFailed": "Update failed: {0}", "removed": "Removed.", "removeFailed": "Remove failed: {0}" },
     "worktreesTab": { "workerOffline": "Worker offline.", "removed": "Removed {0} worktree(s).", "blocked": "Cannot force-remove: {0} task(s) still running. Cancel them first.", "removedFrom": "Removed {0} worktree(s) from {1} task(s).", "cleanupFailed": "Cleanup failed: {0}", "resetFailed": "Reset failed: {0}" },