feat: harden auth for public deploy + gantt, duration units, docker packaging

Security (fail-secure for production):
- Refuse to start without PPM_PASSWORD/PPM_PASSWORD_HASH unless
  PPM_ALLOW_NO_AUTH=1 (local dev only)
- Add login rate limiting (5 failures / 60s per client), enforced inside
  SessionManager.login so it cannot be bypassed at the endpoint layer
- compose defaults PPM_COOKIE_SECURE=true for HTTPS behind reverse proxy
- Add .dockerignore to keep runtime data/out of the image

Features:
- Task timeline gantt on home page (week/month zoom, horizontal scroll,
  infinite-arrow for open-ended dates, CSS Grid layout)
- Duration metrics gain a second/minute/hour unit for input & display
  (canonical storage stays integer seconds)
- Per-metric progress bars on home page (no more merged average)
- Backfill historical records via date picker in the today-record card
- Admin panel: stats overview, JSON import/restore, full task list mgmt

Fixes:
- Nullable task startDate; summarize handles missing start date
- Task dialog cancel/close no longer submits the form
- Import validates whole backup first, rejects path traversal, rebuilds
  archives, and replaces stale files

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/layouts.py

@@ -10,6 +10,7 @@ ALLOWED_COMPONENTS = {
     "task-list",
     "overview-summary",
     "task-progress-grid",
+    "task-gantt",
     "task-header",
     "today-record",
     "metric-progress",
@@ -23,6 +24,7 @@ COMPONENT_SCOPES: dict[str, tuple[tuple[str, ...], str]] = {
     "task-list": (("home", "task-detail"), "sidebar"),
     "overview-summary": (("home",), "main"),
     "task-progress-grid": (("home",), "main"),
+    "task-gantt": (("home",), "main"),
     "task-header": (("task-detail",), "main"),
     "today-record": (("task-detail",), "main"),
     "metric-progress": (("task-detail",), "main"),
@@ -36,7 +38,11 @@ FALLBACKS = {
         "page": "home",
         "regions": {
             "sidebar": [{"component": "task-list"}],
-            "main": [{"component": "overview-summary"}, {"component": "task-progress-grid"}],
+            "main": [
+                {"component": "overview-summary"},
+                {"component": "task-progress-grid"},
+                {"component": "task-gantt"},
+            ],
         },
     },
     "task-detail": {