docs: sync config examples with updated default models (gpt-5, gemini-3.5-flash)

[aheritier]

Documentation updates for recently merged features

This PR brings the /docs content in sync with changes merged into main in the last 36 hours.

Changes

Commit	Source PR	What changed
5dbd717c	#2997	Update 7 code examples in config overview: gpt-5-mini → gpt-5
79b0a736	#2997	Update first_available example: claude-sonnet-4-5 → claude-sonnet-4-6, gemini-2.5-flash → gemini-3.5-flash

Details

docs/configuration/overview/index.md — PR #3003 (merged 2026-06-05) updated the DOCKER_AGENT_DEFAULT_MODEL env var description but left 7 YAML/HCL code examples still showing openai/gpt-5-mini. These are the "Minimal Config", "Inline model card", "Config Versioning", "Reusable MCPs", and "Reusable Commands & Skills" examples — all generic how-to snippets that should use the current default model. The case-sensitivity callout (openai/gpt-5-mini is not the same as openai/GPT-5-mini) is intentionally left unchanged since it references a real valid model.

docs/configuration/models/index.md — The first_available section example used claude-sonnet-4-5 and gemini-2.5-flash as candidates, reflecting the old defaults. Updated to claude-sonnet-4-6 and gemini-3.5-flash to match the current defaults from PR #2997. The Available Models table listing gemini-2.5-flash as a valid model is unchanged.

PRs reviewed and found up to date

Source PR	Reason
#3004	Docs-only PR — all changes applied within the PR itself
#3003	Docs-only PR — partially applied; remaining gaps fixed in this PR
#3001	Internal bugfix (drop orphaned tool results on session resume) — no user-facing documentation impact

[docker-agent]

Assessment: 🟢 APPROVE

All changes in this PR are correct. The diff updates exactly the model references described:

• 7 occurrences of openai/gpt-5-mini → openai/gpt-5 in docs/configuration/overview/index.md
• anthropic/claude-sonnet-4-5 → anthropic/claude-sonnet-4-6 in the first_available example
• google/gemini-2.5-flash → google/gemini-3.5-flash in the first_available example
• claude-sonnet-4-5 → claude-sonnet-4-6 in the named model block

No bugs or logic errors were introduced in the changed lines. The intentionally preserved references (case-sensitivity callout, Available Models table) are consistent with the PR description.