feat(web): protect launcher dashboard with token and SPA login (#1953)

Add token-based authentication for the Launcher's embedded Web Dashboard.

- Ephemeral token generated in-memory each run (or via PICOCLAW_LAUNCHER_TOKEN env var)
- HMAC-SHA256 session cookie (HttpOnly, SameSite=Lax, Secure when HTTPS)
- Bearer token support for API/script access
- Rate limiting on login (10 attempts/IP/min)
- Referrer-Policy: no-referrer on all responses
- POST-only logout with JSON content-type (CSRF-safe)
- System tray "Copy dashboard token" action
- Login page shows contextual help (console/tray/log file path)
- Path traversal protection via path.Clean
- X-Forwarded-Host/Port/Proto support for reverse proxy deployments
- Full i18n support (English, Chinese)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/configuration.md

@@ -67,6 +67,18 @@ PicoClaw stores data in your configured workspace (default: `~/.picoclaw/workspa
 
 > **Note:** Changes to `AGENT.md`, `SOUL.md`, `USER.md` and `memory/MEMORY.md` are automatically detected at runtime via file modification time (mtime) tracking. You do **not** need to restart the gateway after editing these files — the agent picks up the new content on the next request.
 
+### Web launcher dashboard
+
+**picoclaw-launcher** serves a browser UI that requires sign-in first. By default, the **dashboard token** and **session signing key** are **generated in memory on each start** (a new random token after every restart). Set **`PICOCLAW_LAUNCHER_TOKEN`** to pin a fixed token for that process (startup logs do not print the secret when this env var is used).
+
+**Where to read the token**: In **console mode** (`-console`), it is printed at startup. In **tray / GUI mode**, use the tray action **Copy dashboard token**, and check **`$PICOCLAW_HOME/logs/launcher.log`** (typically `~/.picoclaw/logs/launcher.log` if `PICOCLAW_HOME` is unset) for the random token logged on startup. The login page shows hints that match how the launcher is running (including the absolute log path); **responses do not include the token itself**.
+
+- **Config file**: Same directory as `config.json` (or the file pointed to by `PICOCLAW_CONFIG`). The launcher-specific file is `launcher-config.json`.
+- **Sign-in and links**: Enter the token on the login page, or open with `?token=` when the browser is launched automatically. All responses include **`Referrer-Policy: no-referrer`** to reduce leakage of `token` via the `Referer` header.
+- **Sign-out**: Use **`POST /api/auth/logout`** with **`Content-Type: application/json`** (body may be `{}`). Do not rely on a GET URL for logout (CSRF-safe pattern).
+- **Brute-force**: **`POST /api/auth/login`** is **rate-limited per client IP per minute** (HTTP 429 when exceeded).
+- **Session lifetime**: The HttpOnly session cookie lasts about **7 days** by default; sign in again with the token after it expires.
+
 ### Skill Sources
 
 By default, skills are loaded from: