Standup report renderer (ja/en) with golden tests

[Saber5656]

Title

Standup report renderer (ja/en) with golden tests

Summary

Implement the standup Markdown templates (Yesterday / Today / Blockers) for
Japanese and English with per-project one-liners, following DESIGN.md §9.2,
reusing the render infrastructure from 20.

Context

Standup output is the report users paste into team chat — it must be short,
scannable, and safe (redaction footer visible). The one-liner compression
rules here (subjects list truncation etc.) define its character.

Scope

• internal/render/standup.go, templates/standup.ja.md.tmpl,
  templates/standup.en.md.tmpl, goldens, tests.

Detailed Requirements

1. func Standup(r *model.Report) (string, error) — requires
   r.Standup != nil (error otherwise).
2. Structure:
   1. Header: # Standup 2026-07-10 (木) (same weekday/zone rules as 20).
   2. ## 昨日 (2026-07-09) / ## Yesterday (2026-07-09) — the actual
      yesterday-bucket date (Friday on Mondays): per-project bullet:
      - **<project>** — 3 commits: subj1; subj2; +1 more · 2 agent sessions: title1; title2 — rules: ≤ 2 subjects then +N more
      (ja: 他N件), ≤ 2 session titles same rule, segments joined with
      ·, omit absent segments; shell-only activity (no projects) →
      single bullet - shell: N commands / - シェル操作: N件.
      Empty bucket → - (活動記録なし) / - (no recorded activity).
   3. ## 今日 / ## Today — same rules over the today bucket.
   4. ## ブロッカー / ## Blockers — always exactly:
      - (なし — 手動で記入してください) /
      - (none recorded — fill in manually);
      when r.Narrative.Text != "" append subsection
      ローカルLLMの示唆: / Suggested by local model: followed by the
      narrative text block (24 builds standup narratives as
      blocker/summary suggestions; visually attributed, DESIGN §9.2).
   5. Footer: same one-liner as 20.
3. All content through escText/escCell equivalents (bullets are text
   context); subjects/titles use sanitize.Line output already, but
   escaping is still the renderer's responsibility.
4. Goldens: (ja, en) × (typical two-bucket report, empty-yesterday +
   nonempty-today, both-empty, with-narrative) — 8 files.
5. Length discipline: a typical report (3 projects × 4 commits) must fit in
   ≤ 25 lines (asserted on the typical fixture — standup is a summary, not
   a dump).

Acceptance Criteria

• Goldens byte-exact cross-platform; -update supported.
• Monday fixture shows Friday as the yesterday date in the heading.
• Truncation rules (+N more/他N件) exact at boundaries 2 and 3.
• Blockers placeholder always present; narrative subsection only with
  narrative.
• Structural parity test between ja and en (same headings/order).
• Line-count discipline test passes.
• ≥ 90% coverage maintained on the render package.

Validation

go test -race -cover ./internal/render/ in PR; attach ja+en typical
goldens in the PR description.

Dependencies

06, 18, 19, 20 (shared infrastructure).

Non-goals

Collection/wiring (26), automatic blocker detection (v1 non-goal), custom
formats.

Design References

• docs/DESIGN.md §9.2

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Source of truth: docs/issues/21-render-standup.md (PR #1, branch docs/v1-design). If this issue and the repo docs disagree, the docs win. Execution order and dependencies: docs/ISSUE_PLAN.md (this is issue 21 of 33).