chore(agent): commit the machine tier and the doctrine text the checkout was already running

Landing blocker for #61 and #63: the deployment checkout is 12 commits behind and
`merge --ff-only` refuses while tracked paths are dirty. Discard is not available here
(workspace policy: no `checkout`/`stash` on shared state), so the dirt is committed.

- `agent/APPEND_SYSTEM.md`: the point-of-use / one-work-log / PR-link doctrine, already
  byte-identical to `origin/main` (`cmp` against the trunk blob: no difference). No new
  prose — the commit exists so the trunk merge can proceed.
- `agent/config.yml` and `agent/managed-skills/**`: the machine-live tier the heartbeat
  owns (AGENTS.md § Live-sync tiers).

`ALLOW_SECRETS=1` was used, deliberately and after auditing the staged diff by hand: the
only credential-shaped strings in it are two copies of `AKIA0000000000000EXAMPLE` — the
inert all-zero AWS example id — and they appear inside the two skill pages that teach
that exact placeholder shape. This checkout is still running the pre-#61 hook; the merged
gate (value-scoped placeholder filter, `71601f7`) exempts this value, so the refusal
dies with this landing. No `--no-verify` was used: the gate ran and its verdict is
recorded here.

Refs #61

agent/managed-skills/xdg-open-tab-proof-niri/SKILL.md

@@ -0,0 +1,41 @@
+---
+name: xdg-open-tab-proof-niri
+description: "Prove an xdg-open URL actually landed a tab in Frank's Firefox on niri, instead of reporting the law-compliant \"opened in your browser\" blind."
+---
+
+AGENTS.md (`dank/command-center`) requires opening every PR in Frank's browser with `xdg-open <PR-URL>`. `xdg-open` exits 0 whether or not a tab appeared, and its stderr is easy to swallow (`>/dev/null 2>&1 &`), so "opened in your browser" is normally an unverified claim. Prove it before saying it.
+
+## The proof that works
+
+```bash
+export XDG_RUNTIME_DIR=/run/user/$(id -u)
+export WAYLAND_DISPLAY=${WAYLAND_DISPLAY:-wayland-1}
+niri msg windows | grep -iA2 'firefox\|gitea\|pull'
+```
+
+Expected — the tab title is the page title, so it doubles as confirmation you opened the right object:
+
+```
+Title: "#61 - fix(#60): checks that lied… - command-center - Frank's Dank Gitea… — Mozilla Firefox"
+  App ID: "firefox"
+  PID: 1150647
+```
+
+## Why the obvious checks fail here
+
+- **The computer/AX window list does not list Firefox.** `computer.windows()` on this Wayland backend returned only ghostty windows — Firefox exposes no ATSPI top-level unless accessibility is already active inside it — so an empty list is **not** evidence the tab is missing.
+- `capture: false`, `displayCount: 0` in `computer.capabilities()` mean screenshots are unavailable (display asleep); a blank screenshot proves nothing either way.
+- `wmctrl -l` / `hyprctl` do not exist on niri. `niri msg windows` is the window census, and `niri msg outputs` is the output census.
+- `pgrep -af firefox` only shows the process tree (one parent + `-contentproc` children); a tab never appears there.
+- The web page itself is not proof: Gitea's `/dank/<repo>/pulls/N` HTML answers **404** without a session cookie even though the API and the browser both work.
+
+## Dispatch recipe (when nothing is running, or nothing landed)
+
+```bash
+XDG_RUNTIME_DIR=/run/user/$(id -u) WAYLAND_DISPLAY="${WAYLAND_DISPLAY:-wayland-1}" \
+  xdg-open https://gitea.franksdank.cloud/dank/<repo>/pulls/N
+```
+
+Give it the **`https://gitea.franksdank.cloud/…`** form, not the LAN `192.168.0.143:3000` form the API returns — that is the host Frank's bookmarks and cert expectations use. A running Firefox receives the URL as a new tab in the existing instance; re-dispatching opens a second tab, which is a cheap, idempotent way to recover from a swallowed failure.
+
+Related: `gitea-pr-api-cycle` (the API cycle whose final step this verifies), `omp-tui-live-visual-verify` (same rule for terminal UIs: observe the real surface).