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/start/config.md

@@ -0,0 +1,75 @@
+---
+title: Configuration
+description: Config file, environment variables and their precedence.
+---
+
+idx works without configuration. To change defaults, use the config file,
+environment variables or flags. When they disagree, the first one wins:
+
+1. command-line flags
+2. environment variables
+3. the config file
+4. built-in defaults
+
+## Config file
+
+`~/.config/idx/config.toml` (or `$XDG_CONFIG_HOME/idx/config.toml`):
+
+```bash
+idx config init                        # write the defaults below
+idx config set general.output json
+idx config get cache.quote_ttl
+idx config path
+```
+
+```toml
+[general]
+provider = "msn"           # msn | yahoo
+history_provider = "auto"  # auto | yahoo | msn
+exchange = "JK"
+output = "auto"            # auto | table | json | jsonl
+color = true
+
+[cache]
+quote_ttl = 300            # seconds
+fundamental_ttl = 3600
+
+[ownership]
+# db_path = "/path/to/ownership.db"
+# snapshot_manifest = "https://..."
+```
+
+## Environment variables
+
+| Variable | Overrides |
+| --- | --- |
+| `IDX_PROVIDER` | `general.provider` |
+| `IDX_HISTORY_PROVIDER` | `general.history_provider` |
+| `IDX_EXCHANGE` | `general.exchange` |
+| `IDX_OUTPUT` | `general.output` |
+| `IDX_NO_COLOR` | `general.color` (`1` or `true` disables colour) |
+| `IDX_CACHE_QUOTE_TTL` | `cache.quote_ttl` |
+| `IDX_CACHE_FUNDAMENTAL_TTL` | `cache.fundamental_ttl` |
+| `IDX_OWNERSHIP_SNAPSHOT_MANIFEST` | `ownership.snapshot_manifest` |
+| `IDX_CURL_IMPERSONATE_BIN` | path to a `curl_chrome*` binary |
+
+## Files idx keeps
+
+| What | Where |
+| --- | --- |
+| Config | `~/.config/idx/config.toml` |
+| Cache | `~/.cache/idx/` (`idx cache info`, `idx cache clear`) |
+| Ownership database | `~/.local/share/idx/ownership.db` |
+
+The MCP server reads the same config, cache and database.
+
+## Offline and caching
+
+Quotes are cached for `quote_ttl` seconds and fundamentals for
+`fundamental_ttl`. `--offline` makes no network requests and serves cached
+data, even when stale; `--no-cache` always fetches.
+
+:::note
+A config created by `idx config init` before v0.3 pins `output = "table"`.
+Run `idx config set general.output auto` to get JSON when piped.
+:::