feat: plan-mode handshake for interactive review skills

Add a preamble-level STOP-Ask handshake that fires when the user invokes any
of the 4 interactive review skills (plan-ceo-review, plan-eng-review,
plan-design-review, plan-devex-review) while their Claude Code session is
in plan mode. Without this gate, plan mode's "this supercedes any other
instructions" system-reminder outranked the skills' interactive STOP gates
and the skills silently wrote plan files without any per-finding AskUserQuestion.

The handshake offers 2 options (exit-and-rerun, cancel) — the original
third "stay and batch" option was dropped after two independent reviewers
flagged it as a silent bypass of the skills' anti-skip rule.

Architecture decisions (CEO+Eng review):
- Preamble-level resolver, not per-template injection (Codex finding #2)
- Position 1 in preamble composition: after bash block (_SESSION_ID live),
  before onboarding AskUserQuestion gates (so fresh-install users see the
  handshake first, not drowned in telemetry/proactive/routing prompts)
- Generator-only `interactive: true` frontmatter flag, following the
  `preamble-tier` precedent (no host-config frontmatter allowlist edits)
- Host-scoped to Claude via `ctx.host === 'claude'` check inside the
  resolver (simpler than `suppressedResolvers` which only gates `{{}}`
  placeholders)
- One-way-door classification in scripts/question-registry.ts for all 4
  skills so question-tuning `never-ask` preferences can't suppress the gate
- Synchronous telemetry write to ~/.gstack/analytics/skill-usage.jsonl on
  handshake fire (captures A-exit and C-cancel outcomes that terminate the
  skill before end-of-run telemetry runs)

Also adds an explicit STOP block to plan-ceo-review Step 0C-bis so the
approach-selection question can't silently skip to mode selection.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scripts/resolvers/types.ts

@@ -61,6 +61,7 @@ export interface TemplateContext {
   paths: HostPaths;
   preambleTier?: number;  // 1-4, controls which preamble sections are included
   model?: Model;  // model family for behavioral overlay. Omitted/undefined → no overlay.
+  interactive?: boolean;  // true → emit plan-mode handshake in preamble. Generator-only, not written to SKILL.md.
 }
 
 /** Resolver function signature. args is populated for parameterized placeholders like {{INVOKE_SKILL:name}}. */