feat(evals): seedSkills opt-in for PTY slash-command tests + tripwire

Wire ClaudePtyOptions.seedSkills through launchClaudePty: when set (and
hermetic, and no per-test CLAUDE_CONFIG_DIR override), the child gets
hermeticSkillsConfigDir() so typed /skill slash commands resolve instead
of dying as Unknown command before any model turn. Opted in at the three
runPlanSkill* helpers and the four direct-launch slash-command tests
(plan-design-with-ui, plan-ceo-mode-routing, autoplan-chain,
ship-idempotency).

New static tripwire (test/pty-skill-seeding-wiring.test.ts): any test
file that sends a slash command over the PTY must route through a
runPlanSkill* helper or pass seedSkills: true — an unseeded slash-command
test spends money and measures nothing. hermetic-wiring.test.ts now
blesses the repo-tree seeding path explicitly (config dir under runRoot,
symlinks into the repo checkout, never operator ~/.claude).

The CI "Register gstack skills for PTY smoke" step keeps a keep-me note:
container cross-mount symlinks defeat the TUI scanner and HOME is not
hermeticized, so the real-file copies there must survive this change.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit 63c52269daaffb833b3105ea9b4b99be6df8fec7)

test/skill-e2e-ship-idempotency.test.ts

@@ -161,6 +161,7 @@ describeE2E('/ship idempotency E2E (periodic, real-PTY)', () => {
         timeoutMs: 720_000,
         // Disable network-y pieces so the agent can't reach actual github.
         env: { GH_TOKEN: 'mock-not-real', NO_COLOR: '1' },
+        seedSkills: true,
       });
 
       let outcome: 'detected' | 'plan_ready' | 'attempted_mutation' | 'timeout' | 'exited' = 'timeout';