feat: add three-tier model system with Bedrock support

Introduce small/medium/large model tiers so agents use the appropriate
model for their task complexity. Pre-recon uses Opus (large) for deep
source code analysis, most agents use Sonnet (medium), and report uses
Haiku (small) for summarization.

- Add src/ai/models.ts with ModelTier type and resolveModel()
- Add modelTier field to AgentDefinition
- Refactor claude-executor env var passthrough into loop
- Add Bedrock credential validation in preflight and CLI
- Pass through Bedrock and model env vars in docker-compose

docker-compose.yml

@@ -24,6 +24,12 @@ services:
       - ANTHROPIC_AUTH_TOKEN=${ANTHROPIC_AUTH_TOKEN:-}  # Auth token for router
       - ROUTER_DEFAULT=${ROUTER_DEFAULT:-}  # Model name when using router (e.g., "gemini,gemini-2.5-pro")
       - CLAUDE_CODE_OAUTH_TOKEN=${CLAUDE_CODE_OAUTH_TOKEN:-}
+      - CLAUDE_CODE_USE_BEDROCK=${CLAUDE_CODE_USE_BEDROCK:-}
+      - AWS_REGION=${AWS_REGION:-}
+      - AWS_BEARER_TOKEN_BEDROCK=${AWS_BEARER_TOKEN_BEDROCK:-}
+      - ANTHROPIC_SMALL_MODEL=${ANTHROPIC_SMALL_MODEL:-}
+      - ANTHROPIC_MEDIUM_MODEL=${ANTHROPIC_MEDIUM_MODEL:-}
+      - ANTHROPIC_LARGE_MODEL=${ANTHROPIC_LARGE_MODEL:-}
       - CLAUDE_CODE_MAX_OUTPUT_TOKENS=${CLAUDE_CODE_MAX_OUTPUT_TOKENS:-64000}
     depends_on:
       temporal: