feat: make GEMINI_AUTH=oauth authenticate in Docker

OAuth cannot be done interactively in the headless container, so the login
must be seeded into the mounted ~/.gemini. Three problems are fixed:

- Mount fragility on the Windows Docker Desktop target: the creds mount
  defaulted to ${HOME}/.config/javis/gemini, but ${HOME} is often unset when
  compose runs outside a WSL shell, silently mounting the wrong dir. Default is
  now the project-local ./docker/gemini-oauth (cross-platform), GEMINI_OAUTH_DIR
  still overrides.
- No visibility: when oauth is selected but no login is seeded, the path
  silently degraded to DDG/Brave. Added gemini_oauth_ready() + a one-time debug
  hint and a startup entrypoint warning (skipped on the browser role, fail-open).
- Seeding guidance: oauth_creds.json is the essential credential (refresh token;
  GOOGLE_GENAI_USE_GCA=true forces OAuth), which is what the readiness check and
  warning verify; docs recommend copying the whole ~/.gemini for convenience.

Adds docker/gemini-oauth/ seed dir (.gitkeep) with the login files gitignored,
GEMINI_OAUTH_DIR in .env.example, and updates DEPLOY.md, stream_browser_modes.md
and llm_contexts.md. Covered by 3 new tests (10 passed total).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.env.example

@@ -17,6 +17,8 @@ DISCORD_APP_ID=
 DISCORD_GUILD_ID=
 # Voice channel used by the stream-test scripts (bot/scripts/stream-test).
 DISCORD_VOICE_CHANNEL_ID=
+# Optional text channel for posting conversation transcripts (blank = disabled).
+DISCORD_TRANSCRIPT_CHANNEL_ID=
 
 # ---------------------------------------------------------------------------
 # Brain bridge (Python service in bridge/) — STT + reply engine + TTS
@@ -75,6 +77,10 @@ OUTPUT_LANGUAGE=
 # ---------------------------------------------------------------------------
 # Docker desktop (VNC) — used only by the container image
 # ---------------------------------------------------------------------------
+# Host ports the container publishes the VNC + noVNC servers on. Defaults match
+# the compose file (5901 / 6080); override if the host already uses them.
+VNC_PORT=5901
+NOVNC_PORT=6080
 # VNC viewer password (max 8 chars effective). Watch the screen at localhost:5901.
 # Also used by the broadcast keepalive: TigerVNC only refreshes its framebuffer
 # while a VNC client is attached, so the stream keeps a tiny client connected to
@@ -101,6 +107,11 @@ STREAM_BROWSER=true
 GEMINI_AUTH=oauth
 GEMINI_API_KEY=
 GEMINI_MODEL=gemini-2.0-flash
+# OAuth login source for Docker. The container mounts this into ~/.gemini.
+# Default (blank) = ./docker/gemini-oauth (project-local, cross-platform). Seed
+# it once: cp -r ~/.gemini/. docker/gemini-oauth/  (copy the whole login state).
+# Or point at an existing host login instead, e.g. GEMINI_OAUTH_DIR=~/.gemini
+GEMINI_OAUTH_DIR=
 
 # ---------------------------------------------------------------------------
 # VNC screen broadcast