Add ARCHITECTURE + FOLLOWUPS docs and README pointers

Two new docs filling the gaps in the prior set:

docs/ARCHITECTURE.md
- Component map + runtime flow diagrams (install-time and per-stream).
- Cert pipeline walk-through end-to-end (CA bootstrap, op:// references,
  per-host mint, idempotency conditions).
- State directory inventory (where things write at runtime).
- Idempotency contract — explicit rules every script in this repo follows.
- Full file map of the repo.

docs/FOLLOWUPS.md
- Promoted the punch list out of the TROUBLESHOOTING.md trailing section.
- Each item now has: symptom, current workaround, fix sketch (with the
  actual code change, not vague intent), and a complexity estimate.
- Tracks: screensaver inhibit, busiest-workspace auto-switch (2-line
  patch), 1Password black-rectangle workarounds (untested), host.lan
  DNS (out-of-repo), 1P SSH-agent timeout, cert renewal timer, stale
  config keys, single-user assumption.

README.md
- New "Documentation" section between Clients and Diagnostics points at
  each of the three doc files plus client/README.md, with a one-line
  description for each so readers can navigate without spelunking.

README.md

@@ -188,6 +188,15 @@ The host-side installer handles Linux clients via `moonlight-qt`. For everything
 | Android | Play Store: Moonlight Game Streaming. |
 | Apple TV (tvOS) | App Store: Moonlight Game Streaming. |
 
+## Documentation
+
+| Doc | What it covers |
+|---|---|
+| [`docs/ARCHITECTURE.md`](docs/ARCHITECTURE.md) | How the pieces fit together at install time and at stream time; component map; runtime flow diagrams; idempotency contract; file map. |
+| [`docs/TROUBLESHOOTING.md`](docs/TROUBLESHOOTING.md) | Every failure mode hit during the first end-to-end install, in order, with symptom → cause → fix. Custom-keybinding setup for escaping Moonlight on macOS. |
+| [`docs/FOLLOWUPS.md`](docs/FOLLOWUPS.md) | Outstanding work not yet on `main`: screensaver inhibit, busiest-workspace auto-switch, 1Password streaming workarounds, cert renewal automation, stale Sunshine config keys. |
+| [`client/README.md`](client/README.md) | Per-platform Moonlight install and the first-pair walkthrough. |
+
 ## Diagnostics
 
 ```bash