docs: make Bedrock configuration optional for Claude Code (#428)

[aadil79]

Default settings.json now works with plain Claude Code (direct Anthropic API) without Bedrock-specific env vars. Bedrock config moved to an optional section in the README with copy-paste env block.

Fixes #428

Summary

Default settings.json for the Claude harness now works with plain Claude Code (direct Anthropic API) without
requiring Bedrock configuration.

Changes

• Removed Bedrock-specific env vars (CLAUDE_CODE_USE_BEDROCK, AWS_REGION, model IDs) from default
  harness/claude/settings.json
• Changed default model from opus[1m] (Bedrock format) to opus
• Updated README: Bedrock setup moved to an optional collapsible section with copy-paste env block
• Updated general prereqs language to clarify Bedrock is optional for Claude Code

User experience

Before:

Users running plain Claude Code (direct Anthropic API) would hit API errors immediately on first run because
settings.json ships with CLAUDE_CODE_USE_BEDROCK=1 and Bedrock-specific model IDs baked in. The only workaround
was manually editing settings.json to remove these env vars — but the README didn't explain this, making it look
like Bedrock was a hard requirement.

/aidlc --doctor
✻ API error · Retrying in 0s · attempt 4/10

After:

settings.json works out of the box with plain Claude Code — no Bedrock setup needed. Users who want Bedrock can
opt in by adding the env vars from a clearly documented optional section in the README. Both paths work; neither
is broken by default.

Checklist

If your change doesn't seem to apply, please leave them unchecked.

• I have reviewed the contributing guidelines
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented

Test Plan

bun scripts/package.ts --check passes (all harnesses in sync)

Acknowledgment

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