Add context windows, web search, streamed answers, overlay move/resize; overhaul docs

- Context windows (contexts/*.yaml) scope answers to a defined domain
- Optional DuckDuckGo web search behind ai.web_search.enabled (default off)
- Stream partial answers into the overlay at first-token time
- Default Whisper to local base.en (~9x faster); offline model loading
- Priority-ordered loopback detection (BlackHole > Teams device)
- Overlay: drag interior to move, edges to resize
- Stop tracking model binaries (models/ is gitignored)
- README/CLAUDE.md overhaul + tracked config.example.yaml

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

config.example.yaml

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+# Meeting Assistant configuration — copy to config.yaml and edit.
+# (config.yaml is gitignored; it may hold machine-specific/private settings.)
+
+audio:
+  sample_rate: 16000
+  chunk_duration: 2.0
+  vad_threshold: 0.5
+  # Transcription model (local dirs load fully offline — no Hugging Face access
+  # at runtime). base.en is ~9x faster than medium.en on CPU (~0.3s vs ~2.9s per
+  # clip) and is the main latency fix. Switch to models/whisper-medium.en for
+  # more robustness to noise/accents (slower).
+  whisper_model: models/whisper-base.en
+  language: en
+  # "push_to_talk" (hold the key, release to answer) or "continuous" (auto-listen).
+  # Toggle at runtime with ctrl+shift+m.
+  capture_mode: push_to_talk
+  ptt_key: alt_r            # push-to-talk key (Right Option). e.g. cmd_r, f8, ctrl_r
+  source: both              # "microphone", "system", or "both"
+  mic_device: null          # null = auto. Or a device index / name substring.
+  system_device: null       # null = auto-detect loopback. Or index / name.
+  # Devices to try (in priority order) as the "system" source that hears OTHER
+  # participants. A true loopback (BlackHole/Soundflower/VB-Cable) carries ALL
+  # system audio — works for Google Meet, Zoom, Teams, anything. "teams audio"
+  # is Microsoft Teams' own virtual device: zero-install but Teams-only, and it
+  # may be silent outside screen-share; treat it as an experiment.
+  loopback_keywords: ["blackhole", "soundflower", "vb-cable", "loopback", "teams audio"]
+  # Which speakers trigger an answer (others still add transcript context).
+  answer_sources: ["system", "microphone"]
+  # Incremental transcription while the push-to-talk key is held. Off by default:
+  # faster-whisper pads every call to a fixed 30s window, so on small/fast models
+  # this barely helps and can drop words at chunk seams. Enable only with a
+  # large/slow model where the per-call cost is worth amortizing during the hold.
+  streaming_transcription: false
+  # Bias Whisper toward your meeting's vocabulary (optional):
+  # transcription_prompt: "A software engineering interview about Python and Flask."
+
+screen:
+  capture_key: ctrl+shift+space   # press, then drag a box over an on-screen question
+
+hotkeys:
+  toggle_overlay: ctrl+shift+h
+  meeting_summary: ctrl+shift+s
+  toggle_listening: ctrl+shift+m
+
+ai:
+  context_window: 2048
+  max_history: 10
+  model: Qwen2.5-VL-7B-Instruct-Q4_K_M.gguf
+  mmproj: mmproj-Qwen2.5-VL-7B-Instruct-f16.gguf   # required for screen reading
+  answer_mode: auto_obvious   # auto_obvious | auto_all | suggest_only
+  user_name: you
+  # Pin the active context window by file name (contexts/<name>.yaml). If unset,
+  # the first contexts/*.yaml with `active: true` is used.
+  # active_context: python_flask_backend
+  # Optional web search to ground factual answers in current information.
+  # PRIVACY: when enabled, the question text is sent to DuckDuckGo — this
+  # breaks the otherwise fully on-device guarantee. Off by default.
+  web_search:
+    enabled: false
+    max_results: 3
+    timeout: 6.0
+
+overlay:
+  position: top-right
+  font_size: 14