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>

docs-site/download/index.html

@@ -42,11 +42,11 @@
   "@context": "https://schema.org",
   "@type": "SoftwareApplication",
   "name": "OpenCode Mobile",
-  "operatingSystem": "Android 8.0+",
+  "operatingSystem": "Android 7.0+",
   "applicationCategory": "DeveloperApplication",
   "description": "Open-source Android client for the OpenCode AI coding agent. Connect to an opencode server you run yourself and code from your phone.",
   "downloadUrl": "https://github.com/dzianisv/opencode-mobile/releases/latest/download/app-release.apk",
-  "softwareVersion": "0.4.3",
+  "softwareVersion": "0.4.7",
   "license": "https://github.com/dzianisv/opencode-mobile/blob/main/LICENSE",
   "author": { "@type": "Organization", "name": "VIBE TECHNOLOGIES, LLC" },
   "offers": { "@type": "Offer", "price": "0", "priceCurrency": "USD" }
@@ -171,7 +171,7 @@ footer a{margin:0 8px}
       OpenCode Mobile is the free, open-source Android client for the
       <a href="https://github.com/sst/opencode">OpenCode</a> AI coding agent. Install it from
       the F-Droid repository for automatic updates, or grab the signed APK directly.
-      No account, no tracking, no ads. Current version <strong>0.4.3</strong>.
+      No account, no tracking, no ads. Current version <strong>0.4.7</strong>.
     </p>
     <div class="note">
       <strong>Before you install:</strong> OpenCode Mobile is a <em>client</em> — it connects to an
@@ -252,7 +252,7 @@ footer a{margin:0 8px}
     </p>
     <h2>What do I need to run it?</h2>
     <p>
-      An Android 8.0+ device, a machine running <code>opencode serve</code>, a way to reach that machine
+      An Android 7.0+ device, a machine running <code>opencode serve</code>, a way to reach that machine
       from your phone (Tailscale, a Cloudflare/ngrok tunnel, or the same local network), and your own AI
       provider key. The <a href="../guide/">setup guide</a> walks through every step in about 15 minutes.
     </p>