Add battery level reporting (Kconfig-gated) and display orientation

Battery (firmware + server, disabled by default): new battery.c reads
a 2x200k voltage divider via ADC oneshot with curve-fitting calibration
(the ESP32-C6's scheme), maps through a piecewise LiPo discharge curve,
and restores the pin to button duty after each read -- the settled
XIAO ESP32-C6 design shares the back button's GPIO0/A0, time-shared per
wake. Skipped entirely when on mains (a 2x100k VBUS divider into a
spare digital pin -- the 5V pin is dead on battery power, so presence =
mains, where the charging voltage would read misleadingly full) or when
the reading is implausible. The manage overlay gains a battery region
(static outline glyph + "NN%", below the manage QR, all menu levels),
and the device POSTs to the new /frame/battery endpoint after a
successful fetch; the server stores percent + as-of timestamp, exposed
via /api/queue and shown in the web UI. FRAME_BATTERY_ADC_GPIO /
FRAME_VBUS_SENSE_GPIO default to -1 (fully inert on the dev board);
compile-verified both disabled and enabled, hardware bring-up deferred
until the ordered XIAO + batteries arrive.

Orientation (server-side only): new config setting + web UI dropdown
(landscape / portrait / landscape_flipped / portrait_flipped). Photos
are composed/cropped at the logical hanging shape (portrait crops at
480x800, so face-aware crops match how the frame actually hangs), then
rotated losslessly into the panel's native 800x480 byte layout after
dithering -- the device never knows. Face-label anchors are transformed
through the same rotation (logical_to_native()) so they stay attached
to faces on rotated frames. Known documented limitation: the on-device
manage overlay still renders in native orientation, so it appears
sideways on a portrait-hung frame (QRs scan at any rotation; text reads
sideways).

server/app/config.py

@@ -27,6 +27,10 @@ class FrameConfig(BaseModel):
     order: str = "sequential"  # or "shuffle"
     refresh_interval_s: int = 3600
     smart_crop_faces: bool = True
+    # How the physical frame is hung: landscape (native), portrait,
+    # landscape_flipped, portrait_flipped. Purely a server-side render
+    # decision -- the device always receives native 800x480 bytes.
+    orientation: str = "landscape"
 
     # Current photo + upcoming queue (see app/photo_queue.py). current_asset_set_at
     # is what lets the server decide "has it been long enough to advance" on its
@@ -39,6 +43,12 @@ class FrameConfig(BaseModel):
     history: list[str] = []  # bounded stack of previously-current asset ids, most recent last
     excluded_asset_ids: list[str] = []  # permanently removed from this frame's rotation (not deleted from Immich)
 
+    # Last battery report from the device (POST /frame/battery); -1 = never
+    # reported / not battery-powered. battery_as_of mirrors the
+    # current_asset_set_at timestamp pattern.
+    battery_percent: int = -1
+    battery_as_of: float = 0.0
+
 
 def load() -> FrameConfig:
     with _lock: