README down to what a user needs; the rest into docs/

The README had grown to 1,010 lines of user docs and design notes in one file,
and had gone stale: it still showed the old numbered menu, set up only three
providers, and listed preflight checks and a file layout that predate the last
three releases. It now carries install, first run, the full command
reference, the providers at a glance, troubleshooting and a docs index.

docs/:
- providers.md    presets, defaults, the model cache, context windows, each
                  provider (OpenRouter's cost guard and guardrail check are
                  written up for the first time), adding a provider
- live-sessions.md  what a switch does to running sessions, and repair
- design.md       why settings.json, why keys stay out of it (and the vault
                  per platform), the preflight checks as they are now
- bar-widget.md   the widget as it is now: providers from health.json, every
                  server provider's settings, the restart after an upgrade
- architecture.md the pieces, every file on disk and who writes it, the
                  contracts between them, where to change what
- development.md  running the tests, the conventions the code follows,
                  working on the widget, releasing
CONTRIBUTING.md points at it.

Also:
- The per-project session listing used awk, which the CLI avoids because it
  is missing from minimal images; it uses the script's own TSV helpers now,
  and tests/static.sh fails on any awk in the CLI.
- tests/static.sh checks every relative Markdown link and #anchor.
- A unit test pins the managed env keys between cm-json.py and
  claude-mode.ps1, which only a comment kept in step before.
- test_sessions covers the per-project listing, which nothing ran.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/static.sh

@@ -32,6 +32,13 @@ bash_syntax() {
 }
 check 'shell scripts parse (bash -n)' bash_syntax
 
+# awk is absent from minimal images (a stock Fedora WSL rootfs, for one), so the
+# CLI does without it - and one slipped in once, in a listing no test ran.
+no_awk() {
+    ! grep -nw awk linux/claude-mode linux/lib/*.sh 2>/dev/null | grep -vE '^[^:]+:[0-9]+:\s*#'
+}
+check 'no awk in the POSIX CLI' no_awk
+
 check 'python compiles' env PYTHONPYCACHEPREFIX="$tmp" python3 -m py_compile \
     linux/cm-json.py tests/fake_server.py tests/python/test_cm_json.py
 
@@ -118,6 +125,36 @@ if errors:
     sys.exit("\n".join(errors))
 PY
 
+# Relative links, and the #anchors in them, against the headings they point at -
+# so moving a section between files cannot leave a dead link behind. Anchors are
+# slugged the way Gitea and GitHub do: lowercase, punctuation dropped, spaces to
+# dashes.
+check 'Markdown links resolve' python3 - <<'PY'
+import glob, os, re, sys
+def slug(title):
+    title = re.sub(r"`", "", title.strip().lower())
+    return re.sub(r"[^\w\- ]", "", title).replace(" ", "-")
+def anchors(path):
+    text = open(path, encoding="utf-8").read()
+    text = re.sub(r"```.*?```", "", text, flags=re.S)
+    return {slug(m.group(1)) for m in re.finditer(r"^#{1,6}\s+(.+?)\s*$", text, flags=re.M)}
+files = ["README.md", "CONTRIBUTING.md", "CHANGELOG.md"] + glob.glob("docs/*.md")
+errors = []
+for f in files:
+    text = re.sub(r"```.*?```", "", open(f, encoding="utf-8").read(), flags=re.S)
+    for target in re.findall(r"\]\(([^)\s]+)\)", text):
+        if re.match(r"[a-z]+:", target):
+            continue                                  # http:, https:, mailto:
+        path, _, anchor = target.partition("#")
+        dest = os.path.normpath(os.path.join(os.path.dirname(f), path)) if path else f
+        if not os.path.exists(dest):
+            errors.append("%s: %s - no such file" % (f, target))
+        elif anchor and dest.endswith(".md") and anchor not in anchors(dest):
+            errors.append("%s: %s - no heading for #%s" % (f, target, anchor))
+if errors:
+    sys.exit("\n".join(errors))
+PY
+
 QMLLINT="$(command -v qmllint || true)"
 [ -z "$QMLLINT" ] && [ -x /usr/lib/qt6/bin/qmllint ] && QMLLINT=/usr/lib/qt6/bin/qmllint
 if [ -n "$QMLLINT" ]; then