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/scripts/gen-cli-reference.sh

@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+# Writes the CLI reference page from `idx --help` output, walking every
+# subcommand. `nix flake check` runs it against the packaged binary and fails
+# when the committed page is out of date.
+#
+#   web/scripts/gen-cli-reference.sh <idx-binary> > web/src/content/docs/cli/reference.md
+set -euo pipefail
+
+idx=${1:?usage: gen-cli-reference.sh <idx-binary>}
+
+subcommands() {
+  "$idx" "$@" --help | awk '
+    /^Commands:/ { in_cmds = 1; next }
+    in_cmds && /^[^ ]/ { exit }
+    in_cmds && /^  [a-z]/ { if ($1 != "help") print $1 }
+  '
+}
+
+section() {
+  local depth=$1
+  shift
+  local hashes
+  hashes=$(printf '#%.0s' $(seq 1 "$depth"))
+  # shellcheck disable=SC2016 # backticks are Markdown, not command substitution
+  printf '%s `idx %s`\n\n```text\n' "$hashes" "$*"
+  "$idx" "$@" --help
+  printf '```\n\n'
+  local sub
+  for sub in $(subcommands "$@"); do
+    section $((depth + 1)) "$@" "$sub"
+  done
+}
+
+main() {
+cat <<'EOF'
+---
+title: Command reference
+description: Every idx command and flag, generated from idx --help.
+---
+
+<!-- Generated by web/scripts/gen-cli-reference.sh; do not edit by hand. -->
+
+This page is generated from `idx --help`, so it always matches the released
+CLI. For explanations and examples, see the [stocks](/cli/stocks/) and
+[ownership](/cli/ownership/) guides.
+
+## `idx`
+
+```text
+EOF
+"$idx" --help
+printf '```\n\n'
+for group in $(subcommands); do
+  section 2 "$group"
+done
+}
+
+main | sed -e 's/[[:space:]]*$//' -e '${/^$/d}'