feat(web): idx website and user docs (Astro Starlight)

Landing page plus docs for install, quickstart, config, the stocks and
ownership CLI, output and exit codes, the MCP server and per-agent setup,
agent usage, and an agent-led install page (agents/install.md) that a
coding agent follows from a one-line prompt.

- Every docs page is also served as Markdown at <path>.md; llms.txt and
  llms-full.txt come from starlight-llms-txt; a SKILL.md for skill-based
  harnesses is under /skills/idx/.
- The CLI reference and MCP tools pages are generated from idx --help and
  the tools golden; a new web-generated flake check fails when they drift.
- nix develop .#web provides bun; Cloudflare Pages builds web/ on pushes.
- Package homepage metadata points at https://idx.rasyidanaf.com.
- .cloudflare/ (the cf CLI's account cache) is git-ignored.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/content/docs/mcp/index.md

@@ -0,0 +1,56 @@
+---
+title: MCP server
+description: idx-mcp serves idx's stock and ownership data to AI agents over MCP.
+---
+
+`idx-mcp` is a [Model Context Protocol](https://modelcontextprotocol.io)
+server over stdio. It gives an agent the same data as the `idx` CLI, as
+[11 tools](/mcp/tools/): quotes, price history, screening, company data,
+analysis, comparison, and the KSEI ownership queries.
+
+It shares idx's [config, cache and ownership database](/start/config/#files-idx-keeps),
+so `idx ownership sync` in a terminal also feeds the server.
+
+[Set it up in your agent →](/mcp/setup/)
+
+## Results
+
+Tools that fetch live data return:
+
+```json
+{
+  "data": { "...": "the same shape as idx -o json" },
+  "source": "msn",
+  "fetched_at": "2026-10-15T03:20:11Z",
+  "stale": false
+}
+```
+
+`source` is the provider (`msn` or `yahoo`). Results are cached on disk;
+`stale` is true when an expired cache entry was served because a fresh fetch
+failed. Ownership tools return their data directly, from the local
+database.
+
+Errors come back as a tool result with `isError` set and the CLI's error
+body, so the agent can decide whether to retry:
+
+```json
+{"error": true, "code": "PROVIDERUNAVAILABLE", "message": "..."}
+```
+
+## Limits
+
+| Input | Limit |
+| --- | --- |
+| tickers per call (`get_quotes`, `compare_stocks`) | 20, duplicates removed |
+| `screen_stocks` `limit` | 200 |
+| `search_investors` `limit` | 100 |
+| `get_ownership_changes` `limit` | 2000 (default 200) |
+| concurrent tool calls | 4 |
+
+## Ownership data
+
+Ownership tools need a populated database. Either run `idx ownership sync`
+once, or start the server with `--allow-sync`, which adds an
+`ownership_sync` tool so the agent can download the snapshot itself (several
+MB).