fix(skills): address field report findings from issue #13

[robertraf]

Summary

• /implement: Add explicit discovery of ALL test suites (unit, integration, functional) and instruction to inform the user when infrastructure-dependent tests cannot be run
• /review: Add test coverage checklist (new behavior → test, validation → positive+negative test) and gotcha about only running unit tests
• /ship: Add English enforcement rule for commits/PR titles/bodies, add multi-repo safety (verify remote before push), and related gotchas

Context

Issue #13 is a field report from using the full /sdd pipeline on a cross-repo feature. It identified 5 improvement areas. Analysis showed that 2 were already addressed (/tasks English enforcement and immediate branch push) and 1 was partially covered (/implement TDD for behavior changes). The remaining gaps were:

1. /ship had no English enforcement for commits and PR content
2. /implement and /review said "full test suite" but didn't instruct to discover all test projects or handle infra-dependent suites
3. /review lacked a test coverage checklist
4. /ship had no multi-repo remote verification before push

Changes

• skills/implement/SKILL.md: Step 2 now instructs to discover all test suites, run each one, and inform user about infra-dependent tests that can't be run
• skills/review/SKILL.md: Added 3 checklist items for test coverage (new behavior, validation rules, changed code paths) and a new gotcha about only running unit tests
• skills/ship/SKILL.md: Added language rule for English enforcement, added Step 4 remote verification for multi-repo safety, added 2 new gotchas

How to test

• Read each modified SKILL.md and verify the new instructions are clear and actionable
• Verify no existing instructions were removed or contradicted

Closes #13