merge: reconcile PR 40 with current lab

Integrate lab fff55a78 into PR #40 (cc25d5ba). Lab's modular email
backend/frontend, modular settings, split stylesheets (static/style.css
stays deleted), procfs compatibility, and request-scoped TurnContract
authority win; PR #40's routing classifiers, editor/email/task features,
and style.css changes are ported into lab's module and stylesheet homes.

Integration fixes:
- settings/api.js imports ui.js under its canonical versioned URL
- browser observations keep legacy CAPTCHA/access-block evidence
- artifact turns do not re-trigger broad-web research recovery
- env reference documents PR test-tool variables; page regenerated

PR #40 defects surfaced by lab gates and fixed here:
- web_fetch generic schema drops top-level anyOf (OpenAI contract);
  the compact preview contract still requires url or urls
- get_weather registered as a brokered network read
- new lazy editor modules precached for offline use
- SearXNG pin mirrored into GPU standalone compose files
- image model picker again skips offline endpoints

Tests updated where PR #40 changed behaviour on purpose, and PR tests
moved onto lab's document_source helpers.

core/platform_compat.py

@@ -36,6 +36,19 @@ IS_APPLE_SILICON = (
 )
 
 
+# ── procfs ──────────────────────────────────────────────────────────────────
+# Linux exposes one directory per pid under /proc; macOS and Windows have no
+# procfs at all. Any code that walks it must skip the walk rather than raise.
+# Kept as a module attribute so both branches stay testable on either kind of
+# host.
+PROC_ROOT = Path("/proc")
+
+
+def has_procfs() -> bool:
+    """True when the host exposes a procfs pid tree that can be scanned."""
+    return PROC_ROOT.is_dir()
+
+
 # ── File permissions ────────────────────────────────────────────────────────
 def safe_chmod(path, mode: int) -> bool:
     """``os.chmod`` that is a harmless no-op on Windows.