docs: remove beta references from Coder Agents docs and manifest (#27939)

Removes all references to "beta" from the Coder Agents documentation
under `docs/ai-coder/agents/` and the corresponding `"state": ["beta"]`
entries in `docs/manifest.json`. Also updates screenshots, video, and
hero image, and regenerates the auto-generated feature-stages table.

**Beta reference removal:**
- `getting-started.md`: Removed "Coder Agents is in Beta" from the top
note, "is in beta" from the Chats API note, and "during Beta" from the
feedback section. Removed the version/stability note pinning 2.33.1.
- `index.md`: Removed the "Product status" section that stated Coder
Agents is in Beta.
- `manifest.json`: Removed `"state": ["beta"]` from 17 entries for pages
under `docs/ai-coder/agents/`. Preserved all `premium` and `early
access` states.
- `feature-stages.md`: Regenerated the auto-generated beta features
table, which no longer lists Coder Agents.

**Asset updates:**
- `coder-agents-ui.mp4`: Updated demo video on the agents landing page.
- `llm-providers.png`: Updated LLM provider support screenshot.
- `models-list.png`: Updated models list screenshot.
- `models-add-model.png`: Updated add model form screenshot.
- `agents-hero-image.png`: Updated hero image on the `docs/ai-coder`
landing page.

Two references in `models.md` (`v1beta` in the Google Gemini API URL and
`anthropic-beta` in the Anthropic header name) were left unchanged as
they are provider API identifiers, not product status labels.

PR generated with Coder Agents

---------

Co-authored-by: Nick Vigilante <nickvigilante@users.noreply.github.com>

docs/ai-coder/agents/getting-started.md

@@ -3,11 +3,6 @@
 This guide walks platform teams and administrators through setting up Coder
 Agents, preparing your deployment, and running your first Coder Agent.
 
-> [!NOTE]
-> Coder Agents is in Beta. APIs, behavior, and configuration may change
-> between releases without notice; pin a release before broad rollout.
-> Use **Coder version 2.33.1 or greater**.
-
 ## Prerequisites
 
 Before you begin, confirm the following:
@@ -167,10 +162,9 @@ credential scoping, and pre-installing dependencies.
 
 ### Plan for change between releases
 
-Coder Agents is under active development. APIs, behavior, and
-configuration may change between releases without notice. Pin a
-specific release before broad rollout and review the release notes
-before upgrading so changes do not surprise developers in production.
+Coder Agents is generally available.
+However, APIs, behavior, and configuration may change between releases.
+As always, you should review [release notes](https://github.com/coder/coder/releases) and the [changelog](https://coder.com/changelog) before upgrading, so changes do not affect production.
 
 ### Use HTTPS for push notifications
 
@@ -196,7 +190,7 @@ deployment. Use this to encode organizational conventions:
 - Any guardrails specific to your environment.
 
 Configure the system prompt from **AI Settings** > **Coder Agents** > **Instructions**
-or via the API at `PUT /api/experimental/chats/config/system-prompt`.
+or via the API at `PUT /api/v2/chats/config/system-prompt`.
 See [Platform Controls](./platform-controls/index.md) for details.
 
 ### Understand the security model
@@ -256,7 +250,7 @@ This is useful for building automations such as:
 **Quick example — create a Coder Agent via the API:**
 
 ```sh
-curl -X POST https://coder.example.com/api/experimental/chats \
+curl -X POST https://coder.example.com/api/v2/chats \
   -H "Coder-Session-Token: $CODER_SESSION_TOKEN" \
   -H "Content-Type: application/json" \
   -d '{
@@ -269,7 +263,7 @@ curl -X POST https://coder.example.com/api/experimental/chats \
 Stream updates in real time by connecting to the WebSocket endpoint:
 
 ```txt
-GET /api/experimental/chats/{chat}/stream
+GET /api/v2/chats/{chat}/stream
 ```
 
 For service-to-service automation, use
@@ -277,10 +271,6 @@ For service-to-service automation, use
 rather than developer session tokens. Keep automation credentials
 narrowly scoped.
 
-> [!NOTE]
-> The Chats API is in beta and may change without notice.
-> See [Chats API](../../reference/api/chats.md) for the full endpoint reference.
-
 ### Add workspace context with AGENTS.md
 
 Create an `AGENTS.md` file in the home directory (`~/.coder/AGENTS.md`) or
@@ -319,7 +309,7 @@ Good feedback includes:
 - **Context** — screenshots, `chat_id` values, or links to the Agents page help
   the team investigate quickly.
 
-Your input directly influences product direction during Beta.
+Your input directly influences product direction.
 
 ## Next steps