Docs: Document the Dapr Agents Drasi extension (drasi_trigger)

## What content needs to be created or modified?

We need a new integration added under Dapr Agents for the new Drasi extension.

## Describe the solution you'd like
1. Restructure the [Integrations page](https://docs.dapr.io/developing-ai/dapr-agents/dapr-agents-integrations/) into an index.

It's currently one long page. Convert it so each integration is just a title + 1–2 sentence description linking to its own child page. Move the existing content into child pages and add Drasi as a new one:
- Text Splitter
- Arxiv Fetcher
- Vector Stores
- Agents as Tools
- MCP Toolbox for databases
- Drasi (new)

2. Create the Drasi child page. Follow the existing integration convention (Text Splitter, Vector Stores, etc.): teach the API inline with code snippets, not a link-out to a quickstart. Cover:
- What Drasi is and when to use it
- Install: pip install dapr-agents[drasi]
- drasi_trigger usage and configuration (with defaults), shown inline
- Event filtering by operation and view validation
- The DrasiChangeEvent and DrasiOperation models
- A link to the runnable examples/ext-drasi-*-k8s sample for the full deployable version (don't reproduce it in full)

3. Update the [Quickstarts page](https://docs.dapr.io/developing-ai/dapr-agents/dapr-agents-quickstarts/). This page is a table of links to repo samples, not inline tutorials. Add a new row to the Examples table pointing to examples/ext-drasi-*-k8s with a one-line description.

### The associated pull request from dapr/dapr, dapr/components-contrib, or other Dapr code repos

This tracks the docs work for [dapr/dapr-agents#665](https://github.com/dapr/dapr-agents/pull/665), which adds a Drasi extension for DurableAgent. This is an integration that ships dapr_agents.ext.drasi, a one-line drasi_trigger(agent, ...) that lets a DurableAgent consume [Drasi](https://drasi.io/) change events:
- Filters events by Drasi operation (insert / update / delete) and validates them against user-defined models/"views".
- Matching events trigger agent workflow runs with a customizable task payload.
- Public API: drasi_trigger, DrasiChangeEvent, DrasiOperation.
- Installs via pip install dapr-agents[drasi].
- Working examples live in the repo under examples/ext-drasi-*-k8s.

**Additional context**

Done when:
- [ ] Integrations page is an index of title + short description links to child pages
- [ ] Drasi child page created with inline usage (install, drasi_trigger, filtering/validation, models) and a link to the repo example
- [ ] New row added to the Quickstarts "Examples" table for examples/ext-drasi-*-k8s
- [ ] Docs PR opened and linked back on dapr/dapr-agents#665