feat(doctor): report skill plugins the pipelines name but nothing provides

The ship-feature pipelines have always depended on the `superpowers`
plugin — skills/ship-feature/SKILL.md calls its skills by name, and the
node detect rules match `Skill` events named `brainstorming`,
`writing-plans`, `test-driven-development` — but no README, INSTALL,
manifest or SKILL.md said so, and /ccam-doctor did not check. Install the
`ccam` plugin without it and `/ccam:ship-feature-lane` runs partway, then
fails at the first skill call with no warning beforehand.

/ccam-doctor now derives the requirement from the loaded pipeline
templates rather than a hardcoded list: every `/plugin:skill` a template
names, as its own `skill` or as one node's `command`, has to come from an
installed and enabled plugin. Editing a template cannot leave the check
behind, and a custom template in DASHBOARD_PIPELINES_DIR naming some
other plugin is covered for free.

Three deliberate calls:
  - WARN, never FAIL. The dashboard, hooks, CLI and MCP all work without
    it; failing a doctor run over it would cry wolf.
  - A plugin present but explicitly disabled counts as missing — Claude
    Code will not resolve its skills either way.
  - The skills sitting in ~/.claude/skills/ count as satisfied. That is a
    legitimate hand-copied setup, and calling it broken is how a warning
    row teaches its reader to ignore it.

Docs state the prerequisite where someone installing would look: README
and INSTALL requirements, plus docs/PLUGINS.md for how the row decides.
The install line is `superpowers@claude-plugins-official`, verified
present in that marketplace's manifest.

Verified: npm run test:server (1379, +6 covering all three calls above
plus the partially-satisfied case), npm run test:client (459), prettier
and check-headers clean. `node scripts/plugin-doctor.js` here reports
`OK Skill plugins superpowers available`; the WARN branches were checked
against a temp CLAUDE_HOME.

plugins/ccam/commands/ccam-doctor.md

@@ -22,6 +22,9 @@ Print the output verbatim, then add at most three lines of guidance based on the
 - `FAIL MCP build` → `mcp/build/` is out of date; run `npm run mcp:build` in a
   checkout and commit it.
 - `WARN ccam CLI` → print the exact `export PATH=...` line from the output.
+- `WARN Skill plugins` → the pipelines name slash commands no installed plugin
+  provides. The dashboard is unaffected; `/ccam:ship-feature(-lane)` is what
+  stops partway. Print the `claude plugin install …` line from the output.
 - `WARN Dashboard UI` → run `/ccam-open` to build the bundle.
 
 No preamble, no summary of things that passed.