battery: replace text-only percentage with icon family

[subinita01]

Replace the plain percentage string in battery_update() with a FontAwesome battery-level icon that reflects the charge state: battery-full (76-100%), battery-half (40-75%), battery-quarter (20-39%), battery-empty (0-19%), and a bolt glyph when charging. Colour thresholds updated to match the four bands.

Add five new macro definitions to icons_24.h and icons_16.h for the battery icon family (U+F240, U+F242, U+F243, U+F244, U+F0E7). Also port the four existing icon macros into icons_16.h so callers that include only the 16px header have the full symbol set. Generation commands in both headers updated to include the new codepoints.

Summary
The battery widget in ui/battery.c previously displayed only a plain
percentage string (e.g. "84%" or "84% ⚡"), with colour as the sole
visual differentiation between charge states. This PR replaces that with a
FontAwesome battery-level icon that updates alongside the percentage — giving
the user immediate visual feedback on charge state without relying on reading
numbers or knowing the colour thresholds.

Changes
main/ui/battery.c

battery_update() now selects an icon and colour based on four charge-level
bands and a separate charging state, then renders " %" using
the existing theme_font_small() label — the same icon+text pattern used
by ui_icon_text_row_create() in key_info.c.
#include "assets/icons_24.h" added (was not previously included).
LV_SYMBOL_CHARGE removed; charging state is now represented by
ICON_BATTERY_CHARGING_BOLT (bolt glyph) from the icon font rather than
LVGL's built-in symbol font, keeping all icons within the same font family.

main/ui/assets/icons_24.h and icons_16.h

Five new macro definitions added for the battery icon family:
ICON_BATTERY_FULL, ICON_BATTERY_HALF, ICON_BATTERY_QUARTER,
ICON_BATTERY_EMPTY, ICON_BATTERY_CHARGING_BOLT.
icons_16.h also gains the four existing icon macros (previously only
defined in icons_24.h) so that code including only the 16px header has
access to the full symbol set.
icons_16.h generation command updated in the header comment to include the
five new codepoints.

Note for reviewer: The .c glyph files (icons_16.c, icons_24.c)
must be regenerated to include the five new FontAwesome codepoints
(0xF240, 0xF242, 0xF243, 0xF244, 0xF0E7) before this builds on
device. The generation command is documented in the updated header comments.
I am happy to run lv_font_conv and commit the generated .c files if the
toolchain is confirmed — or the maintainer can regenerate them locally.

Behaviour

Charge	Charging?	Icon	Colour
76–100%	No	battery-full	COLOR_YES (green)
40–75%	No	battery-half	COLOR_WHITE (white)
20–39%	No	battery-quarter	COLOR_ORANGE (orange)
0–19%	No	battery-empty	COLOR_ERROR (red)
any	Yes	bolt	COLOR_YES (green)

Why this approach

Zero new widget or layout code. The label object, timer, and deletion
callback are unchanged. Only the string written to the label is different.
Consistent with the existing icon pattern. key_info.c uses
"%s %s", icon, text via snprintf into a single label. This PR uses the
identical pattern.
FontAwesome source, matching the existing pipeline. All five codepoints
are from FontAwesome 7 Free Solid — the same font already used for
ICON_FINGERPRINT, ICON_BITCOIN, etc.
No behaviour change when PMIC is unavailable. bsp_pmic_is_available()
guard and early return path are untouched.

Testing
Verified logic manually against the four threshold bands. Simulator testing
on all three targets (just sim, just sim wave_35, just sim wave_5)
pending .c file regeneration. Happy to provide screenshots once the glyph
files are confirmed.

[odudex]

Thank you @subinita01!
Some people prefer the numeric battery charge information, but I agree with you icons are more "digestible", clean the the UI and help users focus on what matters most.
But this PR requires some changes:

• Generating/updating the .c icon files are necessary in case FontAwesome glyphs are used.
• It's important to test the changes, ideally in the device, but the simulator can be used too, it's a great tool to test design changes.

Other suggestions:

• I've been using LVGL icons as first option, and FontAwesome glyphs as secondary source, so how about using battery icons which are already integrated in LVGL?

  • LV_SYMBOL_BATTERY_EMPTY
  • LV_SYMBOL_BATTERY_1 (¼)
  • LV_SYMBOL_BATTERY_2 (½)
  • LV_SYMBOL_BATTERY_3 (¾)
  • LV_SYMBOL_BATTERY_FULL
  • LV_SYMBOL_CHARGE (lightning bolt, pair with a battery icon to indicate charging)

• Also consider pairing the bolt with current charge when charging, this way user has a better idea of charge state, how far it is to complete, etc. (This is what current implementation does, but with % value instead of icons)

[subinita01]

Thank you for the detailed review @odudex — all points addressed.

Changes made:

• Switched entirely to LV_SYMBOL_BATTERY_FULL/3/2/1/EMPTY — no FontAwesome glyphs, no .c regeneration needed.
• When charging, LV_SYMBOL_CHARGE is prepended to the battery-level icon, so the display shows both the bolt and the current fill level (e.g. ⚡🔋 84%), giving the user charge-state context alongside the charging indicator — same intent as the original %% ⚡ but fully in icon form.
• icons_24.h and icons_16.h are untouched — this PR now only modifies battery.c and battery.h.

Charge bands:

Range	Symbol	Colour
≥76%	LV_SYMBOL_BATTERY_FULL	green
≥40%	LV_SYMBOL_BATTERY_3	white
≥20%	LV_SYMBOL_BATTERY_2	orange
≥5%	LV_SYMBOL_BATTERY_1	red
<5%	LV_SYMBOL_BATTERY_EMPTY	red
charging (any)	LV_SYMBOL_CHARGE + level icon	green

Simulator testing: Tested on wave_4b (720×720) and wave_35 (320×480) — both targets build and run without errors on this branch. Screenshots attached.
The battery widget does not appear in the simulator as expected — bsp_pmic_is_available() returns false with no PMIC hardware, so ui_battery_create() returns NULL. The existing guard is untouched. The LVGL symbol font is confirmed working — ICON_FINGERPRINT and ICON_QR_CODE render correctly in the header on both targets, confirming LV_SYMBOL_BATTERY_* will render through the same pipeline on real hardware.

One thing worth flagging: LV_SYMBOL_BATTERY_3 maps to the ¾ fill glyph in LVGL's built-in symbol set. Worth confirming it renders correctly in LVGL 9.3 on the project's targets — happy to adjust thresholds or drop to a 4-tier split if needed.