fix(funnel): repair activation-path bugs found in end-to-end audit (#114)

Systematic trace of the activation funnel (store listing -> docs setup
guide -> in-app onboarding -> connect flow) after #113 showed a docs
404 bug had slipped through. Fixes found in this pass:

- README.md and CONTRIBUTING.md still told developers to run
  `npm install -g opencode` (missing -ai), the exact 404 #113 fixed
  everywhere else. Same package-name fix applied here.
- src/lib/diagnostics.ts: the health probe reported ok:true for any
  resolved fetch, including 401/403/404/500 responses. A wrong
  password or broken server therefore classified as "Health endpoint
  responded - connection actually works now.", contradicting the
  error shown right next to it. Health now requires a real 2xx;
  root-reachability probe explicitly opts out (requireOk: false) to
  keep its existing reachability-only semantics (already encoded in
  diagnostics-classify.test.ts).
- docs-site/vs-termux: architecture explainer described
  /session/{id}/events and /session/{id}/chat, neither of which
  exists; the app actually uses /global/event and
  /session/{id}/prompt_async (src/lib/sdk.ts).
- docs-site/features: opencode repo link pointed at
  github.com/opencode-ai/opencode instead of github.com/sst/opencode,
  the org used everywhere else in the docs.
- Stale "v0.4.3" version strings (README x3, docs-site/download x2)
  bumped to v0.4.7, the actual latest shipped release confirmed live
  on GitHub Releases and the F-Droid repo index. Fixed the associated
  Android min-OS contradiction (7.0 vs 8.0+) to 7.0, matching the live
  F-Droid manifest's minSdkVersion 24.
- Dropped stale "GPT-4" model naming on 3 docs-site pages, consistent
  with the model-agnostic policy already applied to the Play listing
  in #83.

See PR body for the found-not-fixed list (Play Console listing drift,
GitHub Sponsors not enabled, a Cloud-vs-waitlist messaging conflict)
that need a product/human decision rather than a code fix.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/lib/diagnostics.ts

@@ -36,13 +36,20 @@ export interface DiagnosticReport {
   timestamp: string
 }
 
-async function timedFetch(name: string, target: string, init?: RequestInit): Promise<ProbeAttempt> {
+// requireOk: whether a non-2xx HTTP response counts as a probe failure.
+// The health probe must actually succeed (2xx) to mean "the server works" —
+// otherwise a 401/403/404/500 response was being reported as ok:true, which
+// made classify() short-circuit to "connection actually works now" even when
+// auth failed or the server errored. The root probe only checks reachability
+// (any HTTP response, even an error status, proves something is listening).
+async function timedFetch(name: string, target: string, init?: RequestInit, opts?: { requireOk?: boolean }): Promise<ProbeAttempt> {
+  const requireOk = opts?.requireOk ?? true
   const start = Date.now()
   const controller = new AbortController()
   const timer = setTimeout(() => controller.abort(), PROBE_TIMEOUT_MS)
   try {
     const res = await fetch(target, { ...init, signal: controller.signal })
-    return { name, target, ok: true, status: res.status, durationMs: Date.now() - start }
+    return { name, target, ok: requireOk ? res.ok : true, status: res.status, durationMs: Date.now() - start }
   } catch (error: unknown) {
     const err = error as { name?: string; message?: string; cause?: unknown }
     const aborted = err?.name === "AbortError"
@@ -80,7 +87,7 @@ export async function probeConnection(url: string, auth?: { username: string; pa
     const base = `${parsed.scheme}://${parsed.host}:${parsed.port}`
     ;[health, root, internet] = await Promise.all([
       timedFetch("health", `${base}/global/health`, { headers }),
-      timedFetch("server-root", `${base}/`, { headers }),
+      timedFetch("server-root", `${base}/`, { headers }, { requireOk: false }),
       timedFetch("internet", INTERNET_CHECK_URL),
     ])
   } else {