feat(skills): skill lifecycle + ms-* skill set completion (#40, #41, #42)

- scripts/skill.sh: install (bundled or path) / activate / deactivate /
  uninstall (refuses while enabled) / list
- skills-enabled + skills-available dirs under the data root; a skill not
  in skills-enabled is not enabled or available for use
- pi adapter: MOSAIC_SKILLS -> --skill per dir; --no-skills when none
- agent.sh: seat definitions declare skills[]; resolution against
  skills-enabled refuses the launch loudly when missing
- ms-* skills completed (owner-authored canon, hands-off): ms-tools
  adapted to the runtime, ms-file-read/write/agent/conductor bodies
  written in the owner's style; ms-agent-watch + ms-unslop untouched
- tasks/USER.md onboarding fixtures; suite hardening (nested def path,
  user seed, mock-adapter dispatch evidence)

Suites: config 24, task 74, release 14, conductor 17, verify PASS.
RELEASE 0.0.12 packaged; health-gated activation on merge.

Closes #40, closes #41, closes #42

scripts/test-task.sh

@@ -212,15 +212,20 @@ EOF
     # seat skills dispatch (mock evidence)
     mkdir -p "$SANDBOX/agents/skillseat" "$SANDBOX/data/user"
     printf '# User\n\nname: Jason\n' > "$SANDBOX/data/user/USER.md"
-    printf '{"agentVersion":1,"name":"skillseat","skills":["ms-tools"]}' > "$SANDBOX/agents/skillseat/agent.json"
-    printf '{"agentVersion":1,"name":"skillseat","soulPlaceholder":true}' > /dev/null # no-op
     printf '# SOUL - skillseat\n\nMethodical. Verifies before claiming.\n' > "$SANDBOX/agents/skillseat/SOUL.md"
-    # Pre-align the release pointer so ensure does not fire under the mock
-    # adapter (the gate needs a real model; the mock cannot answer).
+    printf '{"agentVersion":1,"name":"skillseat","skills":["ms-tools"]}' > "$SANDBOX/agents/skillseat/agent.json"
+    printf '# SOUL - skillseat\n\nMethodical. Verifies before claiming.\n' > "$SANDBOX/agents/skillseat/SOUL.md"
+    cat > "$SANDBOX/mock-config.json" <<EOF
+{"configVersion":1,"environment":"development","dataRoot":"$SANDBOX/data","execution":{"backend":"docker","provider":"zai","model":"m","adapter":"mock"}}
+EOF
     REL="$(tr -d '[:space:]' < RELEASE)"
     mkdir -p "$SANDBOX/data/state"
     printf '{"pointerVersion":1,"release":"%s","imageTag":"mosaic-poc-agent:0.84.4-r%s","activatedAt":"2026-01-01T00:00:00Z"}\n' "$REL" "$REL" > "$SANDBOX/data/state/active.json"
-    scripts/agent.sh skillseat </dev/null >"$SANDBOX/seat-stdout.txt" 2>"$SANDBOX/seat-stderr.txt"
+    scripts/skill.sh install ms-tools >/dev/null 2>&1
+    scripts/skill.sh activate ms-tools >/dev/null 2>&1
+    env MOSAIC_CONFIG="$SANDBOX/mock-config.json" MOSAIC_MOCK_RESPONSE=MOCKED \
+        env MOSAIC_AGENTS_DIR="$SANDBOX/agents" \
+        scripts/agent.sh skillseat </dev/null >"$SANDBOX/seat-stdout.txt" 2>"$SANDBOX/seat-stderr.txt"
     RC=$?
     if [ "$RC" -eq 0 ]; then
         PASS=$((PASS+1)); echo "${C_OK}OK${C_RESET}    seat with enabled skill launches"