docs: add Agent Skills bundle for AI agent harnesses

[nicolotognoni]

Summary

• Ship an Anthropic Agent Skills-compliant bundle under skills/ so any compatible AI agent (Claude Code, Claude Desktop, OpenClaw, Hermes, Cursor, Codex, and ~50 others) can learn the Patter SDK end-to-end via npx skills add patterai/patter.
• Five skills + five references covering install, agent build, telephony, tools/handoffs, and call inspection. All code samples are dual Python + TypeScript.
• No SDK runtime changes; this is documentation shipped to the AI agent ecosystem.

Implementation

• Skills shipped (each with YAML frontmatter name + description + license + compatibility + metadata.{author,version,parity}):
  • skills/setup-patter/SKILL.md — install + provider/carrier env keys.
  • skills/build-voice-agent/SKILL.md + references/{realtime-mode,convai-mode,pipeline-mode}.md — pick between OpenAI Realtime 2 (GA), ElevenLabs ConvAI, or the STT→LLM→TTS pipeline.
  • skills/configure-telephony/SKILL.md + references/{twilio,telnyx}.md — carrier setup, webhook URLs, tunnels.
  • skills/add-tools-and-handoffs/SKILL.md — @tool / defineTool, webhook tools, reassurance, transfer_call, end_call, guardrails.
  • skills/inspect-calls-and-metrics/SKILL.md — dashboard mount, CallMetrics, CSV/JSON export, dashboard_token auth.
• Top-level documentation touched: README.md gets an ## Agent Skills section with the install snippet. CHANGELOG.md gets an ### Added entry under ## Unreleased.
• No new dependencies, no runtime impact, no public-API change.
• API surface in the skills verified against the 0.6.2 source: OpenAIRealtime2 is the GA engine, webhook_url lives on the Patter constructor (not serve()), on_call_end is a serve() kwarg receiving a dict, dashboard auth uses dashboard_token (bearer), the metrics store is exposed via phone.metrics_store (Python) / phone.metricsStore (TypeScript), machine_detection defaults to True in 0.6.2, recording is server-wide via phone.serve(recording=True).

Breaking change?

No. Skills are reference content, not a new runtime surface. Existing imports and APIs are unchanged.

Test plan

• find skills -type f -name SKILL.md | xargs -I {} sh -c 'head -1 {} | grep -q "^---$"' — every SKILL.md starts with valid frontmatter.
• For each SKILL.md, the YAML name matches the parent directory name (Anthropic Agent Skills spec requirement).
• description length ≤ 1024 chars for every skill (verified locally — longest is 676).
• Code samples compile/import against getpatter==0.6.2 (Python) and getpatter@0.6.2 (TypeScript). No reference to symbols that don't exist in libraries/python/getpatter/__init__.py or libraries/typescript/src/index.ts.
• No competitor SDK names in source files (only provider integrations we ship: OpenAI, ElevenLabs, Deepgram, Cartesia, Twilio, Telnyx). Compliant with .claude/rules/no-competitor-references.md.
• No internal paths, personal emails, or live secrets in skill text.
• After merge: npx skills add patterai/patter --skill build-voice-agent succeeds on main.

Docs updates

• skills/ — all new (11 files).
• README.md — added "Agent Skills" section between "Templates" and "Configuration".
• CHANGELOG.md — ## Unreleased → ### Added entry describing the bundle.