feat(firmware): integrate kaomoji eyes into animations via eyes_style

[jamro]

Area

Firmware

Problem

#37 added TinyEngineerExpressions and an OLED-only expression-demo, but the library is not used by the robot firmware.

• Existing activity-driven eye modes stay the only on-robot face path.
• Applications and Config cannot choose the kaomoji catalogue without a separate demo flash.
• /anim docs and eye behavior assume classic procedural eyes only (blinks, flicker, X eyes, etc.).

Result: the expression library is optional and isolated; desk-robot animations cannot show those faces.

Proposed change

Integrate #37 faces as a selectable OLED eye style beside classic rounded eyes. Keep animation → servo / audio / RGB unchanged; only the OLED drawer switches.

• Extensible style layer under src/display/eyes/styles/ (EyeStyleRenderer + registry) so later styles do not fork the animation registry.
• New setting eyes_style: classic | kaomoji (NVS, GET/POST /settings, Config). Default classic. Apply immediately.
• When kaomoji, map animation / eye mode / sleep phase → Expression and render() into the shared OLED (never run classic and kaomoji drawers together).
• Reset face playback to elapsed 0 when the expression or style changes (sleep phase, live style switch).
• Docs: qualify classic-specific eye details under /anim; document the kaomoji map; cross-link from eyes_style.

Animation → face map

Animation / phase	Face
none (idle)	Idle
typing, thinking	Thinking
reading, attention	Curious
ring	Surprise
welcome	Happy
error	Angry
abort	Panic
wakeup	Sleepy
sleep / sleep-close	Sleep
sleep-open	Idle
dead	Sad (no classic X)

Acceptance criteria

• eyes_style in NVS + /settings + Config; docs/HTML synced.
• Default classic preserves current eye sequences.
• kaomoji maps all anims; sleep/wake and style switches start at frame 0.
• pio run; validate eyes_style; expression asset checks still pass.
• Bench: live style toggle, anim cycle, sleep/wake; no OLED fights with boot/text.

Out of scope

• Per-anim HTTP face overrides
• Unused faces (Laugh, Wink, Smug, Cry, Shy, Love) unless mapped later
• Servo / audio / RGB changes for this feature

References

• Parent: feat(firmware): add an optional kaomoji expression library #37
• Library: lib/TinyEngineerExpressions/
• Demo: pio run -e expression-demo