Release v0.20.0: /docs/specs surface + nested flyout nav + session body-list removal

Wave 9 follow-up to roadmap item #30 (Session 0017.0 shipped #30 as v0.19.0;
v0.20.0 lands the operator-feedback follow-ups on top).

1. Specs on /docs/specs/<name> (backend docs_specs.py + frontend DocsSpec.jsx
   + DocsSpecsIndex.jsx). Configured via OHM_DOCS_SPECS; framework default
   carries OHM's two specs (rfc-app/SPEC.md + flotilla SPEC.md). Runtime
   fetch from gitea raw with 5-min TTL cache, mirroring docs_sessions.py.

2. Nested flyout nav hierarchy (DocsLayout.jsx). Sessions render as a tree
   with transcripts nested under each session row (labeled by .N ordinal).
   New Specs section between User Guide and Sessions.

3. /docs/sessions/<NNNN> body-list removed (DocsSessionIndex.jsx). Body
   becomes a session-overview card; navigation lives in the left nav.

19 new pytest cases for docs_specs (332 backend total green). Frontend
build clean. Sync frontend/package-lock.json version drift (0.15.0 → 0.20.0)
alongside the VERSION + package.json bump.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/DocsSpec.jsx

@@ -0,0 +1,134 @@
+// DocsSpec.jsx — v0.20.0.
+//
+// Per-spec view at `/docs/specs/:name`. Fetches a configured spec
+// body via the backend mediator (which proxies the gitea raw URL)
+// and renders it through the shared MarkdownPreview. The page header
+// pulls the spec's `title` from the manifest so the breadcrumb-free
+// page still names what you're looking at.
+//
+// Empty-state contract:
+//   404 → "This spec isn't published yet / unknown name" with a hint
+//         to pick a configured spec from the nav.
+//   502 → "Couldn't reach the spec source" + retry button.
+//
+// History view is intentionally absent — the operator's framing for
+// v0.20.0 is "current version only; git is the history surface".
+// A small "View on gitea" link beside the title points at the
+// upstream source URL the manifest carries so the history gesture
+// remains one click away.
+
+import { useEffect, useState, useCallback } from 'react'
+import { Link, useParams } from 'react-router-dom'
+import MarkdownPreview from './MarkdownPreview.jsx'
+import { getSpec, getSpecsManifest } from '../api.js'
+import { EVENTS, track } from '../lib/analytics'
+
+export default function DocsSpec() {
+  const { name } = useParams()
+  const [title, setTitle] = useState('')
+  const [sourceUrl, setSourceUrl] = useState('')
+  const [body, setBody] = useState('')
+  const [status, setStatus] = useState('loading') // loading | ok | notfound | error
+  const [reloadTick, setReloadTick] = useState(0)
+
+  useEffect(() => {
+    track(EVENTS.DOC_VIEWED, { section: `specs/${name}` })
+  }, [name])
+
+  // Title + upstream URL from the manifest (cheap — the manifest is
+  // derived from an env var on the backend, no network).
+  useEffect(() => {
+    let active = true
+    getSpecsManifest()
+      .then(payload => {
+        if (!active) return
+        const entry = (payload && payload.specs || []).find(s => s.name === name)
+        setTitle((entry && entry.title) || '')
+        setSourceUrl((entry && entry.url) || '')
+      })
+      .catch(() => {
+        // Title + source link are decorative; the body fetch below
+        // is the load-bearing one. A failed manifest fetch just
+        // leaves the page rendering the bare name.
+      })
+    return () => { active = false }
+  }, [name])
+
+  useEffect(() => {
+    let active = true
+    setStatus('loading')
+    getSpec(name)
+      .then(text => {
+        if (!active) return
+        setBody(text || '')
+        setStatus('ok')
+      })
+      .catch(e => {
+        if (!active) return
+        if (e.status === 404) {
+          setStatus('notfound')
+        } else {
+          setStatus('error')
+        }
+      })
+    return () => { active = false }
+  }, [name, reloadTick])
+
+  const retry = useCallback(() => setReloadTick(t => t + 1), [])
+
+  const header = title || `Spec: ${name}`
+
+  return (
+    <article className="docs-article">
+      <header className="docs-article-header">
+        <h1 className="docs-article-title">{header}</h1>
+        {sourceUrl && (
+          <a
+            className="docs-source-link"
+            href={sourceUrl}
+            target="_blank"
+            rel="noopener noreferrer"
+            aria-label="View spec source on gitea"
+            data-amp-track-name="Docs Spec Source Link"
+            data-amp-track-spec={name}
+          >
+            View source
+          </a>
+        )}
+      </header>
+      {status === 'loading' && <p className="muted">Loading…</p>}
+      {status === 'notfound' && (
+        <div className="docs-empty">
+          <p>This spec isn't available.</p>
+          <p>
+            <Link
+              to="/docs/user-guide"
+              aria-label="User guide"
+              data-amp-track-name="Docs Spec Notfound User Guide Link"
+            >
+              ← Back to the user guide
+            </Link>
+          </p>
+        </div>
+      )}
+      {status === 'error' && (
+        <div className="docs-error" role="alert">
+          <p>Couldn't reach the spec source.</p>
+          <button
+            type="button"
+            onClick={retry}
+            aria-label="Retry"
+            data-amp-track-name="Docs Spec Retry"
+          >
+            Try again
+          </button>
+        </div>
+      )}
+      {status === 'ok' && (
+        <div className="philosophy-body">
+          <MarkdownPreview content={body} />
+        </div>
+      )}
+    </article>
+  )
+}