docs(web-shot): resolve shot.sh from the install, not a checkout path

The usage block pointed at ~/dev/.skills/web-shot/shot.sh four times. That
directory has not existed since the skills moved into this repo, and the
failure mode is worse than a broken link: web-shot exists for agents with no
local browser, so a 404 sends them to hand-roll the Job instead of looking
harder. One caller burned three attempts on playwright module resolution
before finding the script that documents that exact gotcha.

Replaced with a resolution line covering both delivery paths — the Claude Code
plugin and the ~/.agents/skills symlink — so no absolute checkout path is left
to rot. Verified on koala: resolves to the .agents link, and degrades to an
empty string plus a clear message where the skill is not installed.

The brain entry headless-browser-via-k3s-playwright-job carried the same stale
path in three places and referenced the retired wire-skills.sh wiring; updated
to match.

Closes #26
Bump-Type: patch

skills/web-shot/SKILL.md

@@ -22,18 +22,28 @@ Screenshot a locally-running web UI without installing a browser on the agent's
 
 ## Usage
 
+`shot.sh` ships beside this SKILL.md, so resolve it from wherever the harness
+installed the skill rather than from a checkout path — an absolute `~/dev/...`
+went stale the first time the repo moved and cost a caller three hand-rolled
+Job attempts before they found the working script (#26).
+
 ```bash
+# Claude Code installs the plugin; Crush/Pi/OpenCode get ~/.agents/skills.
+SHOT=$(ls ~/.claude/plugins/marketplaces/*/skills/web-shot/shot.sh \
+          ~/.agents/skills/web-shot/shot.sh 2>/dev/null | head -1 || true)
+[ -n "$SHOT" ] || { echo "web-shot not installed on this host: run install.sh or the plugin install" >&2; exit 1; }
+
 # auto-detect Tailscale hostname, screenshot port 8099 root
-~/dev/.skills/web-shot/shot.sh --port 8099
+"$SHOT" --port 8099
 
 # explicit URL
-~/dev/.skills/web-shot/shot.sh --url http://flamingo:5173
+"$SHOT" --url http://flamingo:5173
 
 # capture a search state too (types into input[name=q])
-~/dev/.skills/web-shot/shot.sh --port 8181 --search agentsquad
+"$SHOT" --port 8181 --search agentsquad
 
 # different output dir
-~/dev/.skills/web-shot/shot.sh --port 3000 --out /tmp/shots
+"$SHOT" --port 3000 --out /tmp/shots
 ```
 
 ## Flags