fix!: prevent AI provider name collision with static settings routes (#26688)

Move the providers routes into a dedicated providers sub-tree: `/ai/settings/providers`, `/ai/settings/providers/add`, and `/ai/settings/providers/:providerId`.

The old `/ai/settings/:providerId` and `/ai/settings/add` URLs are
removed without backward-compatibility redirects. Bookmarked or shared
links to these paths now return a 404. Creating a provider with id `models` (although unlikely) made it impossible to edit it due to a conflict with the static models route.

docs/ai-coder/ai-gateway/providers.md

@@ -30,8 +30,8 @@ handling, and how to monitor providers.
 > configuration that is ineffectual.**
 >
 > The environment variables can be safely removed once seeding has
-> completed. Visit `https://<your-coder-host>/ai/settings` to see which
-> providers have been seeded.
+> completed. Visit `https://<your-coder-host>/ai/settings/providers` to see
+> which providers have been seeded.
 
 After seeding, manage providers through the dashboard or API. A provider
 that has been edited or removed there is not recreated or overwritten

docs/install/releases/esr-2.29-2.34-upgrade.md

@@ -184,7 +184,7 @@ updates, or change administrator expectations:
 | Tasks is the primary AI coding workflow.                                                                        | Coder Agents is the long-term replacement, and Tasks is supported through the 2.34 ESR window (into 2026).                                               | Plan migration from the Tasks API to the Chats API and Coder Agents. See [Migrating from the Tasks API to the Chats API](../../ai-coder/agents/tasks-to-chats-migration.md).                                                                            |
 | AI Gateway injected MCP tools can be used for tool exposure.                                                    | Injected MCP tools are deprecated.                                                                                                                       | Move new integrations toward Coder Agents MCP server configuration or the MCP server flow. See [AI Gateway MCP](../../ai-coder/ai-gateway/mcp.md) and [MCP servers](../../ai-coder/agents/platform-controls/mcp-servers.md).                            |
 | AI Bridge is opt-in via `CODER_AIBRIDGE_ENABLED` (default `false`).                                             | The toggle is renamed to `CODER_AI_GATEWAY_ENABLED` and now defaults to `true`.                                                                          | The in-memory AI Gateway now starts on every deployment. Set `CODER_AI_GATEWAY_ENABLED=false`, or the deprecated `CODER_AIBRIDGE_ENABLED` alias which still works, to keep the old behavior.                                                            |
-| AI Gateway providers are configured with `CODER_AIBRIDGE_PROVIDER_*` or `CODER_AI_GATEWAY_PROVIDER_*` env vars. | Provider configuration is stored in the database. Env vars seed the database once on first startup, then are deprecated.                                 | After upgrade, visit `/ai/settings` to verify seeded providers, then remove the env vars. Coderd fails to start if env vars drift from the seeded database row. See [AI Gateway providers](../../ai-coder/ai-gateway/providers.md).                     |
+| AI Gateway providers are configured with `CODER_AIBRIDGE_PROVIDER_*` or `CODER_AI_GATEWAY_PROVIDER_*` env vars. | Provider configuration is stored in the database. Env vars seed the database once on first startup, then are deprecated.                                 | After upgrade, visit `/ai/settings/providers` to verify seeded providers, then remove the env vars. Coderd fails to start if env vars drift from the seeded database row. See [AI Gateway providers](../../ai-coder/ai-gateway/providers.md).           |
 | Regular users can read their own AI Gateway interceptions.                                                      | Only owners and auditors can read AI Gateway interception data.                                                                                          | Update dashboards, scripts, or user workflows that expected self-service interception reads. This intentionally narrows the RBAC surface.                                                                                                               |
 | `coder groups list -o json` returns the old command output shape.                                               | `coder groups list -o json` returns a flat structure matching other list commands.                                                                       | Update scripts that parse this command output.                                                                                                                                                                                                          |
 | `coder tokens rm` deletes token records by default.                                                             | `coder tokens rm` expires tokens by default and keeps records for auditability.                                                                          | Use `coder tokens rm --delete` only when the token record must be deleted. Update scripts that expect removed tokens to disappear from token history.                                                                                                   |
@@ -257,7 +257,7 @@ The Coder team recommends taking the following steps when performing the upgrade
   starts with changed parameters.
 - **Audit AI Gateway integrations:** Update experimental API routes, check
   permissions for interception/session data, migrate provider configuration
-  from env vars to the database via `/ai/settings`, verify proxy mode behavior,
+  from env vars to the database via `/ai/settings/providers`, verify proxy mode behavior,
   and review any injected MCP usage.
 - **Plan the Tasks to Agents migration:** Tasks remains available during the
   support window, but new automation should use Coder Agents and the Chats API.