feat: add experimental CLI to price unpriced AI models (#27926)

## Description

AI Gateway computes the cost of an interception from `ai_model_prices`,
which is seeded on every server start from a price book embedded in the
binary. A model the price book does not cover records a NULL cost, so
its spend is invisible to cost reporting and is not enforced against
budgets. The only fix was to wait for a Coder release that added the
model.

This adds an experimental CLI, backed by an experimental HTTP endpoint,
for pricing those models. Models the price book already covers are
rejected, because the seeder re-applies the book on every start and
would overwrite an operator price. Support for custom pricing will be
handled in
https://linear.app/codercom/issue/AIGOV-589/extend-experimental-cli-command-to-set-custom-ai-model-prices.

## Commands

```
coder exp ai-model-prices list [--provider] [--model]
coder exp ai-model-prices update [file|-] [--provider] [--model] [--input-price] [--output-price] [--cache-read-price] [--cache-write-price] [--yes]
```

## Changes

- Add `GET` and `POST /api/experimental/ai/model-prices`, gated behind
the AI Bridge entitlement and the existing `ai_model_price` RBAC
resource.
- Add a `GetAIModelPrices` query with optional `provider` and `model`
filters applied in SQL.
- Validate the whole request before writing anything, so one bad entry
cannot leave the table half updated, and report every problem at once.
- Reject prices for models the embedded price book already covers,
through a new `prices.IsDefaultPriced`.
- Add the `coder exp ai-model-prices` command with `list` and `update`.
`update` accepts a JSON document or the single-model flags and prints a
plan, asking to confirm unless the document is piped in or `--yes` is
passed.
- Consolidate the supported provider list into
`coderd/aibridge/prices/providers` so the price generator and the server
share one definition.
- Add `codersdk` types and client methods for both endpoints, and bound
the request body at 1 MiB.
- Document the command in the AI Gateway cost controls page.

Closes
https://linear.app/codercom/issue/AIGOV-567/experimental-cli-command-to-set-prices-for-unpriced-ai-models

> [!NOTE]
> Initially generated by Claude Opus 5, modified and reviewed by
@ssncferreira

docs/reference/api/schemas.md

@@ -1138,6 +1138,58 @@ title: Schemas
 | `last_heartbeat_at` | string | false    |              |             |
 | `name`              | string | false    |              |             |
 
+## codersdk.AIModelPrice
+
+```json
+{
+  "cache_read_price": 0,
+  "cache_write_price": 0,
+  "created_at": "2019-08-24T14:15:22Z",
+  "input_price": 0,
+  "model": "string",
+  "output_price": 0,
+  "provider": "string",
+  "updated_at": "2019-08-24T14:15:22Z"
+}
+```
+
+### Properties
+
+| Name                | Type    | Required | Restrictions | Description |
+|---------------------|---------|----------|--------------|-------------|
+| `cache_read_price`  | integer | false    |              |             |
+| `cache_write_price` | integer | false    |              |             |
+| `created_at`        | string  | false    |              |             |
+| `input_price`       | integer | false    |              |             |
+| `model`             | string  | false    |              |             |
+| `output_price`      | integer | false    |              |             |
+| `provider`          | string  | false    |              |             |
+| `updated_at`        | string  | false    |              |             |
+
+## codersdk.AIModelPriceUpsert
+
+```json
+{
+  "cache_read_price": 0,
+  "cache_write_price": 0,
+  "input_price": 0,
+  "model": "string",
+  "output_price": 0,
+  "provider": "string"
+}
+```
+
+### Properties
+
+| Name                | Type    | Required | Restrictions | Description |
+|---------------------|---------|----------|--------------|-------------|
+| `cache_read_price`  | integer | false    |              |             |
+| `cache_write_price` | integer | false    |              |             |
+| `input_price`       | integer | false    |              |             |
+| `model`             | string  | false    |              |             |
+| `output_price`      | integer | false    |              |             |
+| `provider`          | string  | false    |              |             |
+
 ## codersdk.AIProvider
 
 ```json
@@ -14464,6 +14516,29 @@ If the schedule is empty, the user will be updated to use the default schedule.|
 |--------|--------|----------|--------------|-------------|
 | `hash` | string | false    |              |             |
 
+## codersdk.UpsertAIModelPricesRequest
+
+```json
+{
+  "prices": [
+    {
+      "cache_read_price": 0,
+      "cache_write_price": 0,
+      "input_price": 0,
+      "model": "string",
+      "output_price": 0,
+      "provider": "string"
+    }
+  ]
+}
+```
+
+### Properties
+
+| Name     | Type                                                                | Required | Restrictions | Description |
+|----------|---------------------------------------------------------------------|----------|--------------|-------------|
+| `prices` | array of [codersdk.AIModelPriceUpsert](#codersdkaimodelpriceupsert) | false    |              |             |
+
 ## codersdk.UpsertGroupAIBudgetRequest
 
 ```json