feat(bin): bundle Obsidian MCP server into bin plugin

## Why

The Obsidian MCP server config was living at the repo root, making it
a repo-level concern rather than part of the plugin it belongs to.
Moving it into plugins/bin/ means the plugin is self-contained and the
server travels with it on install.

## Implementation Notes

mcpServers is declared in the Copilot manifest (plugin.json) because
Copilot requires explicit path declarations. CC auto-discovers .mcp.json
from the plugin root so no change to the CC manifest is needed.

---

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/bin/plugin.json

@@ -7,6 +7,7 @@
   "description": "A place for things to be binned",
   "keywords": [],
   "license": "MIT",
+  "mcpServers": ".mcp.json",
   "name": "bin",
   "skills": [
     "skills/"