feat(lanes): give every pipeline node its own driver command

A pipeline template named ONE command for the whole run (`skill`), so the
only way to know what actually moves a given node was to read that node's
`detect` regexes. Each node now carries its own `command`: a slash command
(`/superpowers:writing-plans`) or a shell one (`ccam lanes hook ci-gate`),
whichever its detect rules already watch for.

The values are derived from each node's own detect rules, not invented —
every `ccam …` string was checked against bin/ccam.js and every
`/superpowers:*` against the installed plugin. Nodes reaching which is a
declaration rather than an action (`done`, `merged`, `reported`,
`e2e-feature-passed`, `qc-plan`) are deliberately left empty.

`pipelines.js` normalizes a missing or non-string value to "", so a
custom template written before this field keeps loading rather than
rendering "undefined". `nodeStates()` and GET /api/lanes/pipeline-stats
pass it through. Never executed by the dashboard — display text, the same
contract `skill` already had.

Surfaced where each view has room for it: the Workflows pass-rate panel
shows it under the node label and copies it on click; PipelineMap folds
it into the node tooltip, because a 16-node pipeline has to fit across
one card and there is no width for a second line.

`command?: string` is optional in the client type only to spare four
unrelated test fixtures — the server always sends the key, and the UI has
to branch on the empty string regardless.

Verified: npm run test:server (1373, +3), npm run test:client (459, +2),
tsc --noEmit, prettier and check-headers clean. docs/LANES.md § Custom
template format documents the field. openapi.yaml needs no change: the
lane payload and pipeline-stats were never schematized there.

server/data/pipelines/default.json

@@ -25,6 +25,7 @@
       "label": "Plan",
       "icon": "🧭",
       "gate": false,
+      "command": "/superpowers:writing-plans",
       "aliases": [
         "planning",
         "brainstorm",
@@ -53,6 +54,7 @@
       "label": "Implement",
       "icon": "🛠",
       "gate": false,
+      "command": "/superpowers:test-driven-development",
       "aliases": [
         "implementing",
         "coding",
@@ -77,6 +79,7 @@
       "label": "Tests",
       "icon": "🧪",
       "gate": true,
+      "command": "npm test",
       "aliases": [
         "testing",
         "unit",
@@ -99,6 +102,7 @@
       "label": "Review",
       "icon": "👀",
       "gate": true,
+      "command": "/superpowers:requesting-code-review",
       "aliases": [
         "reviewing",
         "code-review",
@@ -124,6 +128,7 @@
       "label": "Gate",
       "icon": "🚦",
       "gate": true,
+      "command": "/superpowers:verification-before-completion",
       "aliases": [
         "verify",
         "verification",
@@ -146,6 +151,7 @@
       "label": "Ship",
       "icon": "🔀",
       "gate": false,
+      "command": "/superpowers:finishing-a-development-branch",
       "aliases": [
         "pr",
         "pr-open",