docs: fix broken .style/ link and lift details block out of list item [DOCS-661] (#28180)

## What

Two small docs fixes, split out of the offlinedocs Fumadocs migration
(#27390) so that PR stays a focused tooling change and these land on
their own review track.

- `docs/about/contributing/documentation.md`: the Vale style-guide link
pointed at `docs/.style/style-guide/`, which is excluded from the
published docs corpus, so the relative link 404s on the live site.
Repointed to an absolute github.com URL.
- `docs/ai-coder/ai-gateway/monitoring.md`: lifted the "Possible client
values" `<details>` block out of the list item so it renders as a
top-level accordion, and restored a dropped blockquote continuation
marker (`>`).

## Why

Both are genuine docs bugs on their own:

- The `.style/` link is broken on the live site today, because that
directory is intentionally excluded from the published corpus.
- The `<details>` nested inside a list item renders inconsistently;
lifting it to a sibling block is portable across renderers.

They are also prerequisites for the offlinedocs Fumadocs migration,
whose stricter build-time sync hard-fails on unmapped inter-doc links
and only converts a `<details>` to an accordion when it is a list
sibling. Landing them here first lets the migration PR drop these two
files on its next rebase.

## Validation

- `make fmt/markdown` and `make lint/markdown`: clean (via
pre-commit-light).
- Docs-only change; no CI or build config touched.

> This PR was created with AI assistance (Coder Agents).

docs/about/contributing/documentation.md

@@ -33,7 +33,7 @@ following third-party references:
 ## Tools
 
 This repository runs [Vale](https://vale.sh/) on `docs/` as part of CI to enforce prose style.
-The configuration is the repo-root `.vale.ini`, and the curated rule set is documented in [`docs/.style/style-guide/`](../../.style/style-guide/README.md).
+The configuration is the repo-root `.vale.ini`, and the curated rule set is documented in [`docs/.style/style-guide/`](https://github.com/coder/coder/tree/main/docs/.style/style-guide).
 Run the same checks locally with `make lint/prose`.
 Vale runs in advisory mode in this iteration: warnings surface as inline PR annotations, but they don't block the build.
 

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

@@ -197,38 +197,37 @@ curl -X GET "https://coder.example.com/api/v2/ai-gateway/sessions" \
 
 Available query filters:
 
-- `client` - Filter by client name.
-
-  > [!NOTE]
-  > Client classification is done on best effort basis using the `User-Agent` header;
-  > not all clients send these headers in an easily-identifiable manner.
-
-  <br /><details>
-  <summary>Possible <code>client</code> values</summary>
-
-  - `Claude Code`
-  - `Codex`
-  - `Zed`
-  - `GitHub Copilot (VS Code)`
-  - `GitHub Copilot (CLI)`
-  - `Kilo Code`
-  - `Roo Code`
-  - `Coder Agents`
-  - `Mux`
-  - `Cursor`
-  - `OpenCode`
-  - `Charm Crush`
-  - `Junie`
-  - `Unknown`
-
-  </details>
-
+- `client` - Filter by client name. Possible values are listed below.
 - `initiator` - Filter by user ID or username
 - `provider` - Filter by AI provider (e.g., `openai`, `anthropic`)
 - `model` - Filter by model name
 - `started_after` - Filter sessions after a timestamp
 - `started_before` - Filter sessions before a timestamp
 
+<details>
+<summary>Possible <code>client</code> values</summary>
+
+> [!NOTE]
+> Client classification is done on best effort basis using the `User-Agent` header;
+> not all clients send these headers in an easily-identifiable manner.
+
+- `Claude Code`
+- `Codex`
+- `Zed`
+- `GitHub Copilot (VS Code)`
+- `GitHub Copilot (CLI)`
+- `Kilo Code`
+- `Roo Code`
+- `Coder Agents`
+- `Mux`
+- `Cursor`
+- `OpenCode`
+- `Charm Crush`
+- `Junie`
+- `Unknown`
+
+</details>
+
 Refer to the [API documentation](../../reference/api/aigateway.md) for full details.
 
 ## Data retention