Phase 2: Mode A static site — build, serve, search, stage panel

One Go binary serves a pre-rendered site. No Node, no bundler, no node_modules:
htmx and the SSE extension are vendored files, Markdown and code highlighting
run at build time (goldmark + chroma), and the server only writes files.

Implements docs/phase-2-static-site.md:

  2.1 service skeleton   cmd/build (content -> dist), cmd/server (dist -> HTTP),
                         env-configured, 127.0.0.1:8096, /healthz with separate
                         static / ai / search readiness, --health-check probe,
                         deploy/compose.yml + deploy/Dockerfile at 120m
  2.2 rendering          templ components (Layout, Nav, PillarCard, Stage,
                         EvidenceTable, CodeBlock, Timeline, Footer);
                         `make generate` is a build step and is byte-stable
  2.3 navigation         six-area rail, <details> disclosure under 900px,
                         breadcrumbs, aria-current, L1/L2/L3 with artefact pages
  2.4 stage panel        internal/stage owns the contract; RouteDriver (fragment
                         swap) and SSEDriver (event stream) differ only in the
                         Binding, never in layout. fragment ids live in the
                         contract so route files, links and streamed frames agree
  2.5 search             SQLite FTS5 over titles and body, rebuilt by the build;
                         one handler returns a page without HTMX, a fragment with
                         it. Visitors' FTS operators are never honoured
  2.6 quality floor      print stylesheet, JS-off navigation, focus states,
                         semantic landmarks, dark default; security headers

Definition of Done evidence (see issue AUD-142):
  A1  all pages 200 in a network namespace with no external route
  one binary serves the site; make dist writes 45 pages, 86 fragments, 40 docs
  templ generate is deterministic (md5 identical across runs)
  6 L1 + 6 L2 pages, artefact pages reachable in <= 3 clicks
  FTS5 returns sensible hits for zigbee / signage / routing (tested)
  Lighthouse 100 performance and 100 accessibility, mobile and desktop
  first byte well inside 100ms over loopback (test)
  panel renders from a route driver and re-points at the stream untouched
  print legible: /edge/ renders to a 3-page PDF with the print stylesheet

Also fixes found while finishing the build:
  - reject "." / ".." path segments before ServeMux redirects them into a file
    outside the asset directory (/static/../build.json now 404, was 307->200)
  - make test is the real gate: go test ./... plus the validator self-test

internal/stage/stage.go

@@ -38,6 +38,16 @@ const PanelID = "stage-content"
 // PanelTarget is the CSS selector for PanelID.
 func PanelTarget() string { return "#" + PanelID }
 
+// DocFragmentID is the id of the fragment that carries a document's own body.
+// The shape lives here, with the rest of the panel contract, so that a row in an
+// evidence table, a pre-rendered file name and a streamed frame all agree on it.
+func DocFragmentID(docID string) string { return "doc-" + docID }
+
+// ArtefactFragmentID is the id of the i-th artefact in a document. It is
+// derived from the document and the artefact's position, so it stays stable
+// across builds and a saved link keeps working when the content is re-rendered.
+func ArtefactFragmentID(docID string, i int) string { return fmt.Sprintf("art-%s-%02d", docID, i+1) }
+
 // Mode is how a panel receives content.
 type Mode string
 
@@ -77,6 +87,11 @@ type Fragment struct {
 	DocURL     string
 	DocTitle   string
 	Confidence string
+	// Rendered marks Body as a complete fragment: the build already rendered
+	// the article and everything inside it, so a transport writes these bytes
+	// as-is instead of wrapping them again. A source that hands over structured
+	// content leaves it false and the panel renders the fragment normally.
+	Rendered bool
 }
 
 // Binding is everything the Stage component needs to know about its driver.
@@ -293,11 +308,10 @@ func (s *ManifestSource) Stream(ctx context.Context, keys []string, send func(Fr
 		if s.Frame != nil {
 			s.Frame(i)
 		}
-		frag := Fragment{ID: e.ID, Kind: e.Kind, Title: e.Title, Body: templ.Raw(html)}
+		frag := Fragment{ID: e.ID, Kind: e.Kind, Title: e.Title, Body: templ.Raw(html), Rendered: true}
 		if err := send(frag); err != nil {
 			return err
 		}
 	}
 	return nil
 }
-