feat: 4-phase stream lifecycle with live preview before recording

[styu12]

Summary

• Refactor all stream adapters (OAK, OGLO, synthetic demo) from a 2-phase start()/stop() lifecycle to a 4-phase SPI: prepare() → connect() → start_recording()/stop_recording() → disconnect(). This lets the viewer show live camera frames and sensor plots before the user presses Record.
• Add CONNECTING, CONNECTED, and COUNTDOWN session states with a 3/2/1 countdown tick tone before the start chirp.
• New full_rig/ example combining Mac webcam + iPhone + dual OAK + OGLO tactile glove (5 streams on one host).

Changes

• adapters/oak_camera.py: 4-phase lifecycle, XLink enumeration retries for dual-OAK rigs, preview-only capture loop
• adapters/oglo_tactile.py: 4-phase lifecycle, BLE scan matches both device.name and adv.local_name
• types.py: New CONNECTING, CONNECTED, COUNTDOWN session states
• tone.py: Countdown tick spec (100ms C6 beep), sounddevice warning upgraded from INFO → WARNING
• viewer/fonts.py: (new) System font loader for non-ASCII viewer glyphs (●, ■, →, —)
• viewer/app.py: Font loading at startup, session teardown on window close
• viewer/state.py: Filter auxiliary channels (timestamps, _-prefixed) from sensor plot Y-axis
• viewer/demo.py: All synthetic streams converted to 4-phase lifecycle, improved screenshot capture
• discovery/_ble.py: Fixed _cache_lock → _scan_lock bug in clear_cache()
• examples/: New full_rig/ and mac_iphone_dual_oak/ READMEs, updated uv run instructions
• tests/: Updated OAK and OGLO tests for 4-phase lifecycle, added preview vs recording counter tests

Test Plan

• pytest tests/unit/adapters/test_oak_camera.py — 4-phase lifecycle, legacy compat, depth option
• pytest tests/unit/adapters/test_oglo_tactile.py — payload decoding, preview sample isolation
• pytest tests/unit/test_tone.py — countdown tick spec
• Manual: run examples/full_rig/record.py with full hardware rig
• Manual: run examples/mac_iphone_dual_oak/record.py and verify live preview → record → stop → re-record cycle

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