docs: verify follow-up findings before reporting (workflow)

[s2x]

Description

Extends the subagent workflow (docs/workflow.md) so that follow-up findings are verified before being reported — preventing duplicate or unverified issues (as happened in the #176 cycle, where a verification pass found 1 of 4 proposed findings was already covered by #180).

Changes

• New subsection "Follow-up Candidate Verification" (under section 5): subagents must
  1. verify technical truth with file:line evidence (verdicts: CONFIRMED / PARTIALLY TRUE / FALSE — drop FALSE)
  2. scan ALL GitHub issues for duplicates — gh issue list --state all --limit 100 and pagination (--limit 30 is only gh's default, there may be more) + gh search issues keyword search → ALREADY TRACKED verdict with issue number
  3. report one line per finding: verdict, evidence, suggested label
• Section 4 (coder) and section 5 (review): follow-up paragraphs now mandate the verification step; coder's "Final step" prompt extended
• Quick Reference + Notes: updated to reflect the verification step and the pagination reminder

Testing

• Docs-only change — no build/test needed

Code Review

• N/A (docs change, mirrors procedure already executed successfully in the fetch() with outputFields parameter (zvec v0.5.0) #176 cycle — see issues fetch(): expose includeVector + mirror upstream nullable normalization #192/queryVector(): setVamanaParams()/setHnswRabitqParams() create HnswQueryParams — engine rejects query #193/tests: run-tests.php leaves untracked tests/*.php artifacts after failed runs #194 created from verified findings)