fix: case-insensitive agent name lookup in config (fixes #1097)

[octo-patch]

Fixes #1097

Problem

When users configure per-agent model overrides in config.json, the agent name key must exactly match the internal Python class name (e.g. "CodeMonkey", "Importer"). When the case doesn't match (e.g. user writes "code_monkey" or "importer"), the lookup silently falls back to "default" with no warning, making overrides appear to have no effect.

Solution

Made llm_for_agent perform a case-insensitive match when the exact agent name is not found. This allows config keys like "codemonkey", "importer", or "specwriter" to correctly resolve to the "CodeMonkey", "Importer", and "SpecWriter" configurations respectively.

Also updated example-config.json to:

• List all valid agent names in a comment
• Add commented-out examples showing how to override individual agents

Testing

Added a test case test_case_insensitive_agent_lookup that verifies:

• "codemonkey" resolves to the "CodeMonkey" config
• Unknown agent names still fall back to "default"

All 11 existing tests continue to pass.

[CLAassistant]

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0 out of 4 committers have signed the CLA.

❌ Zvonimir Sabljic
❌ github-actions[bot]
❌ LeonOstrez
❌ MarkoBosnjak98

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