feat: scene awareness (P1 + P4)

[chenchaoyi]

Summary

Introduces a scene concept — four named environments (home / office / public / audit) that each carry default knobs and a baseline-expectation prior. Scope of this PR is Phase 1 (scene enum + CLI/env + presence-gate per scene + title-bar chip) and Phase 4 (session_meta JSONL header + analyze consumption + LLM prompt injection). Phases 2 (scenes.yaml persistence + auto-detect) and 3 (other knobs going scene-aware) are deferred to follow-ups, per the user-confirmed plan.

Why

The 2026-05-21 EN ↔ ZH TUI audit + the user's BLE events-modal screenshot showed that one set of defaults can't cover both a home network (sparse, anomalies matter) and a corp office (dense, churn IS the baseline). And when diting analyze --for-llm hands the JSONL to ChatGPT / Claude, the LLM has no idea whether the dense BLE churn it sees is "anomalous" (home) or "expected baseline" (office) — the same data tells different stories under different priors.

Scene catalog

Scene	When to use	ble_presence_gate_s
home (default)	apartment / own Wi-Fi, ≤ ~15 BLE, single AP	5 s — matches v1.5.0 default, no behavioural break
office	corp floor, enterprise Wi-Fi, dense BLE + many BSSIDs	15 s — absorbs Continuity RPA churn baseline
public	cafe / train / plane / public Wi-Fi	30 s — almost everything is passers-by
audit	actively investigating (security / debug / forensics)	0 s — record every advert

Resolution precedence: --scene CLI flag > DITING_SCENE env var > home default. --ble-presence-gate D continues to override the scene's gate.

What's in this PR

• openspec/changes/add-scene-awareness/ — proposal / design / tasks + new scenes capability + 5 delta files (cli / event-log / analyze / bluetooth-scanning / tui-shell)
• src/diting/scene.py — module-level state (mirrors i18n.py pattern), HOME / OFFICE / PUBLIC / AUDIT constants, get_scene / set_scene / resolve_scene / scene_defaults
• src/diting/cli.py — _extract_scene_arg, _resolve_ble_presence_gate(scene_default=...), scene threaded into _run_tui and _run_monitor, help text update
• src/diting/event_log.py — EventLogger.emit_session_meta(scene, scene_source, ssid, gateway_ip), idempotent, first-line-of-session
• src/diting/tui.py — DitingApp accepts scene + scene_source; subtitle chip via _build_subtitle; calls emit_session_meta immediately after constructing the logger
• src/diting/analyze.py — reader collects session_meta into Report.scenes / Report.scene_sources; scene_summary + scene_llm_context_paragraph helpers; render_markdown adds **Scene:** header line; build_llm_prompt prepends [Scene context] paragraph
• src/diting/i18n.py — ZH scene names (家 / 公司 / 公共 / 排查), chip format, error messages, help-text update
• tests/test_scene.py (new) — 16 tests covering resolution, defaults, knob mapping
• tests/test_event_log.py — 5 new session_meta tests (header order, idempotency, null fields, disabled no-op, all-fields)
• tests/test_cli.py — 10 new tests (--scene parse / env / invalid / missing; scene-aware gate resolution)
• tests/test_analyze.py — 11 new tests (session_meta consumption, multi-scene mix, source promotion, Markdown header, LLM prompt context paragraph)
• README.md + docs/zh/README.md — new ## Scenes section
• CHANGELOG.md + docs/zh/CHANGELOG.md — ## [Unreleased] → ### Added, four bullets, EN ↔ ZH parity
• tests/TESTING.md + docs/zh/TESTING.md — new ### scenes section + extended event-log and analyze sections

State machine (per-session)

INIT ──(named OR _connected OR gate=0)──> PRESENT
INIT ──(anonymous advert, gate>0)──> PENDING
PENDING ──(gate elapsed)──> PRESENT  [emit seen]
PENDING ──(TTL eviction before gate)──> INIT  [silent]
PRESENT ──(TTL eviction)──> DEPARTED  [emit left]
DEPARTED ──(re-arrival OR re-eviction)──> DEPARTED  (silent, per #107)

Scene only changes the gate value used in the PENDING → PRESENT transition.

Test plan

• uv run pytest — 826 passed (805 → 826, +21 new)
• uv run python scripts/tui_snapshot.py --mode regression — green; ZH subtitle now renders 视图：Wi-Fi · 扫描间隔 7s · [家] and EN renders view: BLE · [home]
• openspec validate --specs --strict — 21/21 passed
• openspec validate add-scene-awareness --strict — valid
• diting --help + DITING_LANG=zh diting --help both render new --scene entry
• Real-environment smoke: capture a session with --scene office against a corp Wi-Fi, confirm the events panel has the chip + the JSONL has the session_meta line + diting analyze --for-llm injects the office prior

What this PR explicitly does NOT do

• ~/.config/diting/scenes.yaml per-network persistence (Phase 2)
• Auto-detect heuristic on first launch + "new network detected" banner (Phase 2)
• Other knobs going scene-aware: roam_notify_threshold, bonjour_categories_visible, lan_inventory_default, event_throttle (Phase 3)
• Basics modal "Scenes" section (Phase 2)

These were intentionally scoped out to keep the PR reviewable and to validate the four-scene catalog in real use before locking in more surface.

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