Document v0.6.0 changes in CHANGELOG and docs (#311)

Wrap-up for the v0.6.0 release: capture features/BC breaks merged since
v0.5.0 that were missing from documentation.

- CHANGELOG: add the `title` field on `Resource`/`ResourceTemplate` (#301),
  a feature plus three positional-argument BC breaks.
- mcp-elements.md: add the missing `title` parameter to the McpTool,
  McpResource, McpResourceTemplate and McpPrompt attribute reference
  sections; fix a missing closing paren in an `#[McpPrompt]` example.
- server-builder.md: add `title?` to the `addPrompt()` row of the method
  reference table (stale since v0.5.0).
- client.md: bump the protocol-version example to `V2025_11_25` to match
  the new default.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -273,6 +273,8 @@ $client->connect($transport);
 - **[Transports](docs/transports.md)** — STDIO and HTTP transport setup and usage
 - **[MCP Elements](docs/mcp-elements.md)** — Creating tools, resources, prompts, and templates
 - **[Server-Client Communication](docs/server-client-communication.md)** — Sampling, logging, progress, and notifications
+- **[Protocol Extensions](docs/extensions.md)** — Opt-in protocol extensions announced during capability negotiation, including MCP Apps (HTML UI resources)
+- **[Authorization](docs/authorization.md)** — OAuth and authorization setup for HTTP transport
 - **[Events](docs/events.md)** — Hooking into server lifecycle with events
 
 ### Learning & Examples