docs: rename AI Bridge to AI Gateway and Agent Boundaries to Agent Firewall (#24094)

*Disclaimer: implemented by a Coder Agent using Claude Opus 4.6*

## Summary

Renames product references across documentation:

| Old Name | New Name |
|----------|----------|
| AI Bridge | AI Gateway |
| AI Bridge Proxy | AI Gateway Proxy |
| Agent Boundaries | Agent Firewall |

## What changed

- Prose text, headings, titles, and descriptions updated across all docs
- Directories renamed:
  - `docs/ai-coder/ai-bridge/` → `docs/ai-coder/ai-gateway/`
- `docs/ai-coder/ai-bridge/ai-bridge-proxy/` →
`docs/ai-coder/ai-gateway/ai-gateway-proxy/`
  - `docs/ai-coder/agent-boundaries/` → `docs/ai-coder/agent-firewall/`
- All internal markdown links updated to new paths
- `manifest.json` route paths updated
- Rename notice added to AI Gateway and Agent Firewall entrypoint pages

## Companion PR

URL redirects (old paths → new paths):
[coder/coder.com#700](https://github.com/coder/coder.com/pull/700)

## What is intentionally NOT changed

- **Env vars**: `CODER_AIBRIDGE_*`
- **CLI flags**: `--aibridge-*`
- **API paths**: `/api/v2/aibridge/*`
- **Config keys**: `aibridge:` YAML blocks
- **Terraform variables**: `enable_aibridge`, `boundary_version`,
`use_boundary_directly`
- **Process names**: `aibridged`, `aibridgeproxyd`
- **Prometheus metrics**: `coder_aibridged_*`, `coder_aibridgeproxyd_*`
- **SDK types**: `codersdk.AIBridge*`
- **GitHub URLs**: `github.com/coder/aibridge`
- **Image paths**: `images/aibridge/`
- **Auto-generated reference docs**: `docs/reference/cli/aibridge*.md`,
`docs/reference/api/aibridge.md`, `docs/reference/api/schemas.md`
- **Frontend code**: `site/src/` references (separate PR)

Code-level renames (env vars, configs, frontend) are planned for a
follow-up PR.

docs/ai-coder/tasks.md

@@ -15,7 +15,7 @@ The Task details view shows the user's complete chat, workspace status and, buil
 ![VS Code IDE Extension Details View](../images/guides/ai-agents/vs_code_tasks_extension_details.png)
 
 > [!NOTE]
-> Both Community and Premium deployments include 1,000 Agent Workspace Builds for proof-of-concept use. Community deployments do not have access to [AI Bridge](./ai-bridge/index.md) or [Agent Boundaries](./agent-boundaries/index.md). To scale beyond the 1,000 build limit or enable AI Governance features, the [AI Governance Add-On](./ai-governance.md) provides expanded usage pools that grow with your user count. [Contact us](https://coder.com/contact) to discuss pricing.
+> Both Community and Premium deployments include 1,000 Agent Workspace Builds for proof-of-concept use. Community deployments do not have access to [AI Gateway](./ai-gateway/index.md) or [Agent Firewall](./agent-firewall/index.md). To scale beyond the 1,000 build limit or enable AI Governance features, the [AI Governance Add-On](./ai-governance.md) provides expanded usage pools that grow with your user count. [Contact us](https://coder.com/contact) to discuss pricing.
 
 ## Supported Agents (and Models)