Trim skill redundancies surfaced by self-review of #1067

Net -83 lines across the four skill files touched by 694ef0c.

auto-pipeline (-79):
- Collapse Step 0a + 0b into a single picker block; the only
  difference was "filter by number" vs "sort and pick top" — now
  branched by whether the ISSUE env var is set.
- Extract the boilerplate that was duplicated across all five
  subagent prompts (output-only-JSON-block contract, universal don'ts,
  malformed-JSON retry policy, severity vocabulary) into a single
  "Subagent Contract" section near the top. Each prompt now states
  only its scope and JSON shape. Drop the trailing "Reporting
  Contract" section (merged into the new one).
- Trim the Board states table from 8 GraphQL IDs to the 3 columns
  the orchestrator actually writes (ready, on-hold, plus the Backlog
  it reads in Step 0). The IDs for In Progress / Review pool /
  Under review / Final review live in run-pipeline / review-pipeline
  where they are used.
- Drop three rows from Common Mistakes that just echoed the spec
  (codex retry cap, increment SUBSTANTIVE_RETRIES, re-check after
  auto-fix); keep only the non-obvious cross-cutting traps.

check-issue (-9 net):
- Rule Check 5a no longer re-lists the literature fallback chain;
  one-line reference to Check 3c suffices.
- Rule Check 5c verdict table drops the (severity: ...) annotations
  on Fail rows — severity classification is owned by auto-pipeline's
  Subagent Contract, not by check-issue itself.
- Rule Check 5c drops the "cited reference does not contain the
  reduction" row that explicitly admitted overlap with Check 3c;
  add a one-line note that 3c handles that case.

review-structural (-19):
- Step 4b-4 (pred --via spot-check) was hedged out of its own
  purpose with a "fall back to 4b-2" escape hatch. Rewrite as a
  short focused step that uses pred --via when wired and is skipped
  (with a note) otherwise — no padding.

review-quality (~2 net):
- Replace the 4-criterion expansion of the round-trip rule (which
  was copy-pasted from review-structural Step 4b-3) with a single
  pointer to that source-of-truth section. Per the existing
  feedback_skill_no_duplication memory.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: isPANN