docs: update documentation, add future tasks, and fix debug endpoint security

- **Documentation Overhaul**:
  - **README.md**: Restructured installation guide to align with Nextcloud 33+ paths (e.g., "Personal Settings → Security"), added curl examples, updated known limitations, and added a "Future Features" section.
  - **agent.md**: Updated architecture documentation to reflect `TalkService.php` growth (1138 to 1904 lines), updated constructor parameters, and corrected method documentation (e.g., `buildRichObject` now creates TYPE_ROOM shares, `postToRoom` uses query params).
  - **architecture.md**: Added notes regarding the admin gate for the debug endpoint.

- **New Files**:
  - Added `Future to-do.md` to track planned features (inbound messages, filtering, etc.).
  - Added `TODO.md` to track pending tasks and code cleanup.

- **Code Fixes**:
  - **lib/Controller/WebhookController.php**: Re-applied `#[AdminRequired]` attribute to the `debug()` method to enforce admin authentication.
  - **lib/Service/TalkService.php**: Updated docblock for `buildRichObject` to clarify it creates TYPE_ROOM shares.
  - **lib/Settings/Admin.php** & **templates/adminSettings.php**: Corrected bot password generation instructions to point to the correct Nextcloud settings path.

- **Configuration**:
  - **appinfo/info.xml**: Bumped version to 1.2.1 and updated `max-version` to 35.

appinfo/info.xml

@@ -5,7 +5,7 @@
     <name>nc_bot_webhooks</name>
     <summary>Discord webhook bridge for Nextcloud Talk with image support</summary>
     <description>Accepts Discord webhook-style JSON payloads and posts them into Nextcloud Talk rooms, preserving image attachments. Each room gets its own webhook URL with an auth token for security.</description>
-    <version>1.2.0</version>
+    <version>1.2.1</version>
     <licence>AGPL-3.0-or-later</licence>
     <author homepage="https://emberlab.ca">Kyle</author>
     <namespace>Ncbotwebhooks</namespace>