docs(agents): add pr-review and triage-prs skills, always-on communication guidance

- pr-review: maintainer-proxy verdict review (decline / push-back /
  merge-then-fix / merge) with ready-to-post actions, product-fit
  escalation, ache salvage on declines, and merge-base diff measurement
- triage-prs: batch queue triage pipeline (mechanical sweep, duplicate
  clusters, fan-out verdict reviews, approved batch actions) with
  canonical message templates
- AGENTS.md: new Communication section replaces the always-load
  communication-style mandate; the skill keeps a trigger-based
  description for editing human-facing text
- register all project skills in .claude/skills (only 6 of 17 were
  linked, leaving most skills undiscoverable)

.claude/skills/changelog-authoring

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+../../.agents/skills/changelog-authoring

.claude/skills/communication-style

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+../../.agents/skills/communication-style

.claude/skills/desktop-shell

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+../../.agents/skills/desktop-shell

.claude/skills/openchamber-change-discipline

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+../../.agents/skills/openchamber-change-discipline

.claude/skills/performance-engineering

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+../../.agents/skills/performance-engineering

.claude/skills/pr-review

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+../../.agents/skills/pr-review

.claude/skills/relay-transport

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+../../.agents/skills/relay-transport

.claude/skills/serve-sim

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+../../.agents/skills/serve-sim

.claude/skills/sync-state-invariants

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+../../.agents/skills/sync-state-invariants

.claude/skills/triage-prs

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+../../.agents/skills/triage-prs

.claude/skills/writing-for-agents

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+../../.agents/skills/writing-for-agents