feat(#195): chat attachment support for files and images (#418)

* feat(#195): add chat attachment support for files and images

- Add Attachment data model with computed properties (isImage, formattedSize, fileExtension)
- Extend ChatMessage with optional attachments list
- Add Coil 2.7.0 for async image loading in Compose
- Extend ChatViewModel with pending attachment state, addAttachment/removeAttachment/clearAttachments
- Build attachment-prefixed message text (data URIs for images, file refs for others)
- Add paperclip button and file picker launcher (ActivityResultContracts.GetContent) to ChatScreen
- Add animated attachment preview chips with thumbnails before sending
- Render attachments inline in UserBubble (AsyncImage for images, file cards for others)
- Add string resources for attachment UI features

* fix(#195): rewrite attachment upload protocol to match Hermes backend RPC methods

BREAKS: removes old buildAttachmentText() that embedded base64 data URIs in prompt text.

Changes:
- Replace inline data-URI encoding with proper backend RPC flow:
  - image.attach_bytes for images (fire-and-forget, auto-queues to session)
  - file.attach for non-image files (awaited, returns @file: ref text)
- Add CompletableDeferred to PendingRequest so sendMessage can await RPC responses
- Add readContentUriBytes() to read file content from content:// URIs
- Add sendRpcAndAwait() suspend function for sequential RPC calls
- Add RpcCallException for awaited RPC error handling
- Suppress error UI for awaited RPCs (caller handles them directly)
- Keep ChatScreen/ChatBubble UI layer unchanged (file picker, previews, inline images)

* feat(#195): add camera capture support via FileProvider + TakePicture contract

- Creates temporary photo files in cacheDir via FileProvider
- Launches system camera with ActivityResultContracts.TakePicture
- Adds camera icon button (📷) next to the paperclip in ChatInputBar
- Captured photos added as image/jpeg attachments via same addAttachment flow
- FileProvider configured with cache-root path in res/xml/file_paths.xml
- Error handling for launch failures and capture failures with snackbar

* refactor(#195): group camera/image/file into single attach dropdown

- Replaces separate 📷 and 📎 buttons with a single 📎 button
- DropdownMenu opens with three options:
  - 📷 Camera → TakePicture via FileProvider temp URI
  - 🖼️ Image → GetContent("image/*")
  - 📄 File → GetContent("*/*")
- Removes onAttachClick, adds onImageTap/onFileTap callbacks
- Input bar stays clean with one attachment affordance

* fix(#195): add missing imports for CI compilation

ChatScreen.kt:
- android.util.Log
- androidx.compose.animation.core.* (infiniteRepeatable, tween, LinearEasing, RepeatMode, rememberInfiniteTransition)
- androidx.compose.foundation.layout.widthIn
- androidx.compose.material.icons.filled.AttachFile
- androidx.compose.material.icons.filled.InsertDriveFile
- androidx.compose.ui.layout.ContentScale
- coil.compose.AsyncImage

ChatBubble.kt:
- androidx.compose.material.icons.filled.InsertDriveFile

* fix(#195): resolve android-lint LocalContextGetResourceValueCall error

Replace context.getString(R.string.chat_camera_error) with a
composable-level cameraErrorMsg captured via stringResource()
to avoid querying resources via LocalContext.current in a callback.

* fix(#195): migrate InsertDriveFile to AutoMirrored, fix chip double-remove

- Replace deprecated Icons.Filled.InsertDriveFile with
  Icons.AutoMirrored.Filled.InsertDriveFile in ChatBubble.kt
  and ChatScreen.kt
- Remove onClick from AttachmentChip Surface so only the
  dedicated close button triggers removal, not accidental taps
  on the chip body

---------

Co-authored-by: Hermes Agent <hermes@agent.local>

app/src/main/AndroidManifest.xml

@@ -37,6 +37,16 @@
         <receiver
             android:name=".notification.NotificationReplyReceiver"
             android:exported="false" />
+
+        <provider
+            android:name="androidx.core.content.FileProvider"
+            android:authorities="${applicationId}.fileprovider"
+            android:exported="false"
+            android:grantUriPermissions="true">
+            <meta-data
+                android:name="android.support.FILE_PROVIDER_PATHS"
+                android:resource="@xml/file_paths" />
+        </provider>
     </application>
 
 </manifest>