v2.6.2 — Default Opus 5

Default Opus model bumped to Claude Opus 5 across all providers following Anthropic's release.

Provider	--opus / --high resolves to
Anthropic API / Pro	claude-opus-5
AWS Bedrock	global.anthropic.claude-opus-5 (global inference profile)
Vertex AI	claude-opus-5
Azure Foundry	claude-opus-5 (default deployment name)
Vercel AI Gateway / OpenRouter	anthropic/claude-opus-5

Overridable per provider via CLAUDE_MODEL_OPUS_{AWS,VERTEX,ANTHROPIC,AZURE,VERCEL} and ROUTER_MODEL_HIGH.

• --fable/--best (Claude Fable 5) remains the top tier above Opus — tier ordering unchanged.
• Vertex region overrides gain VERTEX_REGION_CLAUDE_5_OPUS; _4_6/_4_7/_4_8 kept for back-compat.
• Docs updated to reference Opus 5 (README, help text, secrets.example.sh, and the airun-docs site).

Upgrade with ai update.