fix(#2636): surface gsd-sdk query failures and add workflow↔handler parity check (#2656)

* fix(#2636): surface gsd-sdk query failures and add workflow↔handler parity check

Root cause: workflows invoked `gsd-sdk query agent-skills <slug>` with a
trailing `2>/dev/null`, swallowing stderr and exit code. When the installed
`@gsd-build/sdk` npm was stale (pre-query), the call resolved to an empty
string and `agent_skills.<slug>` config was never injected into spawn
prompts — silently. The handler exists on main (sdk/src/query/skills.ts),
so this is a publish-drift + silent-fallback bug, not a missing handler.

Fix:
- Remove bare `2>/dev/null` from every `gsd-sdk query agent-skills …`
  invocation in workflows so SDK failures surface to stderr.
- Apply the same rule to other no-fallback calls (audit-open, write-profile,
  generate-* profile handlers, frontmatter.get in commands). Best-effort
  cleanup calls (config-set workflow._auto_chain_active false) keep
  exit-code forgiveness via `|| true` but no longer suppress stderr.

Parity tests:
- New: tests/bug-2636-gsd-sdk-query-silent-swallow.test.cjs — fails if any
  `gsd-sdk query agent-skills … 2>/dev/null` is reintroduced.
- Existing: tests/gsd-sdk-query-registry-integration.test.cjs already
  asserts every workflow noun resolves to a registered handler; confirmed
  passing post-change.

Note: npm republish of @gsd-build/sdk is a separate release concern and is
not included in this PR.

* fix(#2636): address review — restore broken markdown fences and shell syntax

The previous commit's mass removal of '2>/dev/null' suffixes also
collapsed adjacent closing code fences and 'fi' tokens onto the
command line, producing malformed markdown blocks and 'truefi' /
'true   fi' shell syntax errors in the workflows.

Repaired sites:
- commands/gsd/quick.md, thread.md (frontmatter.get fences)
- workflows/complete-milestone.md (audit-open fence)
- workflows/profile-user.md (write-profile + generate-* fences)
- workflows/verify-work.md (audit-open --json fence)
- workflows/execute-phase.md (truefi -> true / fi)
- workflows/plan-phase.md, discuss-phase-assumptions.md,
  discuss-phase/modes/chain.md (true   fi -> true / fi)

All 5450 tests pass.

commands/gsd/thread.md

@@ -38,7 +38,7 @@ ls .planning/threads/*.md 2>/dev/null
 For each thread file found:
 - Read frontmatter `status` field via:
   ```bash
-  gsd-sdk query frontmatter.get .planning/threads/{file} status 2>/dev/null
+  gsd-sdk query frontmatter.get .planning/threads/{file} status
   ```
 - If frontmatter `status` field is missing, fall back to reading markdown heading `## Status: OPEN` (or IN PROGRESS / RESOLVED) from the file body
 - Read frontmatter `updated` field for the last-updated date