feat(cost): tagged Bedrock application inference profiles

**Context:** ROADMAP.md → Optional tagged application inference profiles
**Related:** #215

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## Component

CDK / infrastructure

## Describe the feature

CDK-managed **Bedrock application inference profiles** per onboarded repo or environment. Set `ANTHROPIC_MODEL` to tagged profile ARN for `resourceTags/*` billing when repo count is bounded.

## Use case

When IAM session-tag attribution (#215) is insufficient or repo count is small, tagged inference profiles provide an alternative chargeback dimension in CUR.

## Proposed solution

1. Blueprint optional `inference_profile_arn` override.
2. CDK creates profiles with `resourceTags` for `repo`, `environment`.
3. Agent/runtime config resolves model ARN at task start.
4. Document operator setup and profile limits in `docs/design/COST_MODEL.md`.
5. Fallback to default model when profile unset.

## Other information

- Complements #215; not a replacement for in-app `cost_usd`.
- Design context: `docs/design/COST_MODEL.md`.

- [ ] This might be a breaking change

Start with ROADMAP.md and docs/design/COST_MODEL.md, then trace the CDK blueprint and agent/runtime configuration entry points. Review the related IAM session-tag issue (#215) and Bedrock profile limits. Done means optional per-repo or per-environment profiles are supported, unset profiles fall back to the default model, and operator setup is documented.

Written by the indexing model from the issue text.