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

dotfiles/noctalia/.local/state/noctalia/settings.toml

@@ -275,13 +275,13 @@ transition = [ "fade" ]
     interval_seconds = 1200
 
     [wallpaper.default]
-    path = "/home/blank/.local/share/noctalia/wallpapers/wallhaven_v93dk3.jpg"
+    path = "/home/blank/.local/share/noctalia/wallpapers/wallhaven_g7r3vd.jpg"
 
     [wallpaper.last]
-    path = "/home/blank/.local/share/noctalia/wallpapers/wallhaven_v93dk3.jpg"
+    path = "/home/blank/.local/share/noctalia/wallpapers/wallhaven_g7r3vd.jpg"
 
     [wallpaper.monitors.DP-1]
-    path = "/home/blank/.local/share/noctalia/wallpapers/wallhaven_v93dk3.jpg"
+    path = "/home/blank/.local/share/noctalia/wallpapers/wallhaven_g7r3vd.jpg"
 
     [wallpaper.monitors.DP-2]
     path = "/home/blank/.local/share/noctalia/wallpapers/wallhaven_oxex69.jpg"
@@ -290,7 +290,7 @@ transition = [ "fade" ]
     path = "/home/blank/.local/share/noctalia/wallpapers/wallhaven_v9e2w3.jpg"
 
     [wallpaper.monitors.eDP-1]
-    path = "/home/blank/.local/share/noctalia/wallpapers/wallhaven_v93dk3.jpg"
+    path = "/home/blank/.local/share/noctalia/wallpapers/wallhaven_g7r3vd.jpg"
 
 [weather]
 unit = "imperial"