Optimize the issue skill family

[potiuk]

Part of #1342 — apply the setup-family optimization recipe to the issue family.

8 skills, 47,006 body tokens in total; 1 over the 200-token always-on budget, 6 over the 5,000-token body budget.

skill	body tokens (budget 5,000)	always-on tokens, est. (budget 200)	lines (cap 500)
issue-stale-sweep	6,422 ⚠	~208 ⚠	580 ⚠
issue-triage	8,515 ⚠	~176	797 ⚠
issue-reproducer	6,548 ⚠	~197	585 ⚠
issue-fix-workflow	6,177 ⚠	~183	574 ⚠
issue-backlog-stats	6,137 ⚠	~193	520 ⚠
issue-reassess	5,668 ⚠	~197	515 ⚠
issue-deduplicate	4,542	~193	459
issue-reassess-stats	2,997	~156	319

Body tokens are from docs/mode-economics.md; always-on figures are a chars ÷ 4 estimate of description + when_to_use. ⚠ marks a budget exceeded. Line counts include the generated pre-flight block.

Order of work (per the umbrella):

1. Trim the frontmatter of every skill marked ⚠ in the always-on column.
2. Split any over-cap body, moving sub-action-specific rules into sibling files byte-for-byte.
3. Wording pass on the rest, with headings, golden-rule headlines, code blocks and the pre-flight block kept byte-identical.
4. Run each touched skill's eval suite before and after, outside the sandbox.

Record any inconsistencies found but not fixed (eval-coupled wording, stale headings) in the PR description.

[liwenjie200543]

Taking this one, following the #1342 recipe (same as #1390 for pr-management): trim the always-on frontmatter first, split over-budget bodies into sibling files byte-for-byte, then a wording pass. Headings, golden-rule headlines, code blocks and eval-extracted sections stay byte-identical.