docs: add OpenChamber feature docs and translations (#1400)

* docs: add OpenChamber feature docs and translations

Add 30 new docs pages covering OpenChamber-specific workflows and setup:
OpenCode server, providers/models/agents, MCP, skills, commands & snippets,
usage, projects, context, notes/todos/plans, scheduled tasks, project actions,
preview, worktrees, multi-run, git & GitHub, magic prompts, git identities,
mobile/PWA, security, notifications, voice, project icons, remote instances,
desktop browser, updates, and three troubleshooting pages.

Rebuild sidebar into eight task-oriented sections and translate every new
page into all six supported locales (uk, zh-cn, es, pt-br, ko, pl).

* docs: surface new sections on homepage and cross-link tunnels

Add an Explore block to the docs homepage (all seven locales) linking to
the new section anchors, and cross-link the Tunnels page to Security and
PWA & Mobile.

packages/docs/content/docs/project-icons.mdx

@@ -0,0 +1,20 @@
+---
+title: Project Icons
+description: Give each project a recognizable icon.
+---
+
+# Project Icons
+
+A project icon makes it easy to tell your projects apart at a glance. OpenChamber tries to find one for you, and you can always set your own. Manage it at **Settings → Projects**.
+
+## Automatic discovery
+
+When you add a project, OpenChamber looks for a `favicon` file inside it and uses that as the project's icon. If your repo already ships a favicon, the icon usually just appears — nothing to do.
+
+## Set your own
+
+Open **Settings → Projects** and upload an image (PNG, JPEG, or SVG, up to 5 MB). A custom image takes priority over the auto-discovered one. You can also pick a color instead, or remove the image to fall back to discovery.
+
+## Related
+
+- [Projects](/projects/) — name, color, and organize your projects