Widget system Phase 1: per-type render/action modules

New app/widgets/ package (photos.py, calendar.py, whiteboard.py, plus
the WIDGET_TYPES registry) -- the widget-system analogue of
routers/device.py's old RENDERERS/ADVANCE_RENDERERS/BACK_RENDERERS,
generalized from "one mode owns the whole panel" to "each widget renders
into its own region and responds to named button actions." Each module
exposes render(db, frame, widget, target_w, target_h) -> Image.Image
(never raises -- a widget's own fetch hiccup falls back to a small
placeholder rather than taking the whole panel's render down) and an
ACTIONS registry for NEXT/BACK button assignment.

Supporting changes needed to give the widget modules something to call,
all mechanical/behavior-preserving for every existing caller:

- image_pipeline.py: render_panel(regions, ...) generalizes render_frame's
  tail (paste, enhance once, overlay once, quantize once, pack once) from
  one photo to N regions -- not a restructuring, since calendar mode's
  photo-inlay feature already pastes a second composed image onto the
  canvas before that single shared pipeline runs.
- photo_queue.py: advance_forced/back_forced/remove_from_rotation/
  get_current take an explicit `frame` param now that `cfg` won't always
  be the Frame itself once photo-queue state moves to PhotoWidgetConfig
  -- caught a real latent bug while doing this: get_current was reading
  refresh_interval_s off `cfg`, but that's a frame-level wake-cadence
  setting, not something that becomes per-widget, so it now reads that
  off `frame` explicitly instead.
- routers/common.py: list_assets/fetch_source_and_faces take album_id/
  display_mode directly instead of a whole Frame (both only ever read
  that one attribute off it); new get_or_refresh_*_for_widget siblings
  of the existing calendar/weather/tasks/whiteboard cache helpers, read/
  writing the new per-widget config tables -- the Frame-scoped originals
  are untouched and still what routers/device.py's actual dispatch calls
  until the Phase 2 cutover.

26 new tests (95 total): render_panel size/placement/orientation
coverage, and per-widget-type render/action tests (unconfigured ->
placeholder, a fetch failure -> placeholder not a crash, actions mutate
the right state). Full suite passes; diff-reviewed to confirm
device.py's actual RENDERERS dispatch and the old Frame-scoped
get_or_refresh_* bodies are unchanged, so this is safe to deploy on its
own despite being step 1 of a two-step cutover (see the project plan on
why the *next* step, not this one, has to ship atomically).

server/tests/test_widgets_calendar.py

@@ -0,0 +1,102 @@
+"""app.widgets.calendar -- unit-level, no HTTP: constructs Widget/
+CalendarWidgetConfig rows directly and monkeypatches the underlying
+fetch calls (get_or_refresh_*_for_widget), which have their own
+dedicated fetch/merge test coverage elsewhere (test_calendar_feed.py
+etc.) -- this file is about the widget wiring itself: does render()
+produce a correctly-sized image, do advance/back move browse_offset."""
+
+from __future__ import annotations
+
+import time
+
+from app import widgets
+from app.db import widget_locked
+from app.models import CalendarWidgetConfig, Frame, Widget
+
+
+def _make_widget(db_session, **cfg_kwargs) -> tuple[Frame, Widget]:
+    frame = db_session.get(Frame, 1)
+    widget = Widget(frame_id=frame.id, widget_type="calendar", x=0, y=0, w=8, h=5,
+                    sort_order=0, created_at=time.time())
+    db_session.add(widget)
+    db_session.flush()
+    db_session.add(CalendarWidgetConfig(widget_id=widget.id, **cfg_kwargs))
+    db_session.commit()
+    return frame, widget
+
+
+def _stub_fetches(monkeypatch, events=None, weather=None, tasks=None):
+    monkeypatch.setattr(widgets.calendar, "get_or_refresh_calendar_events_for_widget",
+                        lambda db, frame, widget: (events or [], ""))
+    monkeypatch.setattr(widgets.calendar, "get_or_refresh_weather_for_widget",
+                        lambda db, frame, widget: weather or [])
+    monkeypatch.setattr(widgets.calendar, "get_or_refresh_tasks_for_widget",
+                        lambda db, frame, widget: tasks or [])
+
+
+def test_render_produces_a_correctly_sized_image(db_session, monkeypatch):
+    frame, widget = _make_widget(db_session, view="agenda")
+    _stub_fetches(monkeypatch)
+
+    img = widgets.calendar.render(db_session, frame, widget, 400, 300)
+    assert img.size == (400, 300)
+    assert img.mode == "RGB"
+
+
+def test_render_resizes_when_target_differs_from_full_panel(db_session, monkeypatch):
+    """Phase-1 calendar widgets are still full-panel-layout internally
+    (see app/widgets/calendar.py's own module docstring) -- resizing to
+    fit whatever target box is asked for keeps render_panel's contract
+    (exact target_w x target_h) satisfied even before real small-widget
+    layout support lands."""
+    frame, widget = _make_widget(db_session, view="week")
+    _stub_fetches(monkeypatch)
+
+    img = widgets.calendar.render(db_session, frame, widget, 250, 150)
+    assert img.size == (250, 150)
+
+
+def test_weather_only_fetched_when_enabled(db_session, monkeypatch):
+    frame, widget = _make_widget(db_session, view="agenda", weather_enabled=False)
+    calls = []
+    monkeypatch.setattr(widgets.calendar, "get_or_refresh_calendar_events_for_widget",
+                        lambda db, frame, widget: ([], ""))
+    monkeypatch.setattr(widgets.calendar, "get_or_refresh_weather_for_widget",
+                        lambda db, frame, widget: calls.append(1) or [])
+    monkeypatch.setattr(widgets.calendar, "get_or_refresh_tasks_for_widget",
+                        lambda db, frame, widget: [])
+
+    widgets.calendar.render(db_session, frame, widget, 400, 300)
+    assert calls == []
+
+
+def test_tasks_only_fetched_for_week_view_when_enabled(db_session, monkeypatch):
+    frame, widget = _make_widget(db_session, view="agenda", tasks_enabled=True)  # not week view
+    calls = []
+    monkeypatch.setattr(widgets.calendar, "get_or_refresh_calendar_events_for_widget",
+                        lambda db, frame, widget: ([], ""))
+    monkeypatch.setattr(widgets.calendar, "get_or_refresh_weather_for_widget",
+                        lambda db, frame, widget: [])
+    monkeypatch.setattr(widgets.calendar, "get_or_refresh_tasks_for_widget",
+                        lambda db, frame, widget: calls.append(1) or [])
+
+    widgets.calendar.render(db_session, frame, widget, 400, 300)
+    assert calls == []  # agenda view -- tasks never shown, so never fetched
+
+
+def test_advance_action_increments_browse_offset(db_session):
+    frame, widget = _make_widget(db_session, view="week", browse_offset=0)
+    widgets.calendar.ACTIONS["advance"](db_session, frame, widget)
+    cfg = db_session.get(CalendarWidgetConfig, widget.id)
+    assert cfg.browse_offset == 1
+
+    widgets.calendar.ACTIONS["advance"](db_session, frame, widget)
+    cfg = db_session.get(CalendarWidgetConfig, widget.id)
+    assert cfg.browse_offset == 2  # accumulates, doesn't reset-then-increment
+
+
+def test_back_action_decrements_browse_offset(db_session):
+    frame, widget = _make_widget(db_session, view="week", browse_offset=3)
+    widgets.calendar.ACTIONS["back"](db_session, frame, widget)
+    cfg = db_session.get(CalendarWidgetConfig, widget.id)
+    assert cfg.browse_offset == 2