Evolve BLE tab into Connection tab with default-layer and OS-detection support

[cormoran]

Summary

Renames the BLE tab to Connection (IconPlugConnected, tab id connection) and extends it to integrate three ZMK modules:

Module	Subsystem identifier	Status
zmk-module-ble-management	cormoran_ble	already integrated, UI carried over unchanged
zmk-feature-os-detection	cormoran__os_detection	new
zmk-feature-default-layer	cormoran__default_layer	new

UI sections (top to bottom)

• Header — Connection title + refresh button that reloads all three subsystems and layer names.
• Status strip — current effective OS (OsBadge), active connection, and resolved default layer.
• Output Priority — unchanged from the BLE tab, including the disconnect warning dialog.
• Connections — USB card (connected state, detected OS, default-layer select) followed by BLE profile cards. Each paired profile card keeps all existing ble-management controls (rename, switch, unpair, active highlight) and gains a second row with an OS override select (Auto / Windows / macOS / Linux / iOS / Android, with a detected: X caption when overridden) and a default-layer select (Unset / OS detection / <layer names>).
• Per-OS Default Layers — one row per OS (Unknown/Windows/macOS/Linux/iOS/Android) with layer selects; the current OS row is highlighted.
• Help box — notes that BLE OS detection is heuristic and links the three module repos.

Graceful degradation

Every subsystem is optional and every section renders only if its subsystem exists, with per-section hints instead of a full-page block:

• ble-management missing → existing hint card kept, but USB card and simple "BLE profile N" rows are still built from default-layer endpoints / os-detection profiles (pure merge helper, unit-tested) so layer/override config still works.
• default-layer missing → Per-OS section body becomes an availability hint linking zmk-feature-default-layer.
• firmware built without OS detection (os_detection_available=false) → per-OS selects disabled with a hint linking zmk-feature-os-detection.
• OS enum conversion between the raw zmk_os (default-layer proto) and the os-detection proto enum (protoOs = zmkOs + 1) is centralized in src/lib/osDetection.ts.

Implementation

• Protos copied to proto/cormoran/{os_detection,default_layer}/ with committed buf-generated code in src/proto/.
• New hooks: useOsDetection (auto-load + 5s poll, no notifications in firmware), useDefaultLayer (set responses carry full state, applied directly without refetch), useLayerNames (lightweight keymap-name fetch).
• New components: OsBadge, LayerSelect.
• Demo transport: stateful demo-os-detection.ts / demo-default-layer.ts handlers registered in demo.ts, so the demo UI is fully interactive; also fixed inverted isOpen flags in the demo BLE fixtures.
• All user-facing strings go through t() with Japanese translations.

Test coverage

• useOsDetection / useDefaultLayer hook tests: encode/decode, sentinel handling (-1/-2), set→state update semantics, 5s polling and cleanup on unmount.
• mergeConnectionCards unit tests covering all subsystem-availability combinations and label priority.
• ConnectionPage tests (17): carried-over BLE behaviors (switch/unpair/rename with 31-char limit), status strip, OS override firing SetBleOverride with the correct enum, per-OS selects disabled when os_detection_available=false, USB card, and BLE rows derived without ble-management.
• npm run lint, npm test (27 suites, 234 passed / 1 pre-existing skip), and npm run build all pass. Manually verified in demo mode: all sections render and select changes round-trip through the demo handlers.

🤖 Generated with Claude Code

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_{Deployed from commit 8b0b358}