fix(evals): align plan-eng/design plan-mode + finding-floor smokes to their declared periodic tier

The #2077 demotion of these four stochastic tests to 'periodic' was inert:
E2E_TIERS declared periodic but the files self-gated on EVALS_TIER === 'gate',
so they kept running in the blocking gate lane and never in the weekly lane.

Flip the four self-gates to 'periodic' (headers/describe labels updated), add
a free static tier-alignment invariant test (dep-list filename mapping;
unmapped self-gated files are reported, never silently skipped), and name the
two plan-mode test files in their own touchfiles dep lists so the invariant
binds for them.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/skill-e2e-plan-eng-plan-mode.test.ts

@@ -1,5 +1,5 @@
 /**
- * plan-eng-review plan-mode smoke (gate, paid, real-PTY).
+ * plan-eng-review plan-mode smoke (periodic, paid, real-PTY).
  *
  * See test/skill-e2e-plan-ceo-plan-mode.test.ts for the shared assertion
  * contract. This file exercises the same contract against /plan-eng-review.
@@ -12,7 +12,7 @@ import {
   assertReportAtBottomIfPlanWritten,
 } from './helpers/claude-pty-runner';
 
-const shouldRun = !!process.env.EVALS && process.env.EVALS_TIER === 'gate';
+const shouldRun = !!process.env.EVALS && process.env.EVALS_TIER === 'periodic';
 const describeE2E = shouldRun ? describe : describe.skip;
 
 // SEED_PLAN_FORCING_FINDINGS: 8+ files + custom-vs-builtin smell forces the
@@ -45,7 +45,7 @@ Ignore Bun's native --shard flag because we want full control.
 None planned — will add later.
 `;
 
-describeE2E('plan-eng-review plan-mode smoke (gate)', () => {
+describeE2E('plan-eng-review plan-mode smoke (periodic)', () => {
   test('reaches a terminal outcome (asked or plan_ready) without silent writes', async () => {
     const obs = await runPlanSkillObservation({
       skillName: 'plan-eng-review',