feat(plugin): ship the repo's skills as ccam plugin skills

The repo root already IS the `ccam` plugin root (`"source": "./"`), so the
conventional `skills/` dir at the root is the plugin's skills dir — while
`.claude/skills/` only loaded for a session whose cwd was inside this
checkout. That is useless for a lane working in another repo, which is why
`ccam skills install` existed at all.

Move all seven skills to `skills/`: they now reach every plugin user as
`/ccam:<name>` (bare `/<name>` as an alias). `ccam skills install` stays as
the fallback for a plain checkout without the plugin, sourcing from the new
path.

Agents deliberately do NOT move. A plugin agent is addressed as
`ccam:qc-local`, which would break the `subagent_type: qc-local` references
in ship-feature-lane; `ccam lanes agents install` keeps writing them into the
lane's own `.claude/agents/`, the highest-priority agent source. MCP was
already plugin-shipped via `plugins/ccam/.mcp.json`.

Mechanical fallout: ~115 source files carry a doc-comment pointer to
`.claude/skills/file-headers/`, repointed to `skills/file-headers/`. The
generic Claude Code config-surface examples in openapi/cc-config (`.claude/
skills/code-reviewer`) describe any user's layout and are left alone.

Also fixes the two file-headers scripts, whose `ROOT=` climbed four levels
from `.claude/skills/file-headers/scripts/` and would have escaped the repo
from the new depth — it scanned sibling projects until corrected to three.

npm run test:server (1160 pass), test:client (422 pass), mcp:typecheck,
mcp:build + mcp:check-build all green.

skills/file-headers/scripts/check-headers.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# check-headers.sh — audit the repo for applicable source files missing the
+# mandatory copyright/authorship header (see skills/file-headers).
+# Prints each non-compliant file; exits 0 when fully compliant, 1 otherwise.
+# @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../../.." && pwd)"
+AUTHOR_MARK="@author Nguyễn Ngọc Trí Vĩ"
+
+missing=0
+while IFS= read -r f; do
+  if ! grep -q "$AUTHOR_MARK" "$f"; then
+    echo "MISSING HEADER: ${f#"$ROOT"/}"
+    missing=1
+  fi
+done < <(
+  find "$ROOT" \
+    \( -name node_modules -o -name dist -o -name build -o -name .git \
+       -o -path "$ROOT/data" -o -path "$ROOT/monitoring/.bin" \
+       -o -path "$ROOT/monitoring/.data" -o -name "__snapshots__" \) -prune -o \
+    -type f \( -name "*.js" -o -name "*.ts" -o -name "*.tsx" -o -name "*.cjs" \
+       -o -name "*.mjs" -o -name "*.py" -o -name "*.sh" -o -name "*.css" \) \
+    ! -name "*.min.js" -print
+)
+
+if [ "$missing" -eq 0 ]; then
+  echo "✔ All applicable files carry the authorship header."
+fi
+exit "$missing"