Implement comprehensive metadata extraction for raster images with

EXIF support and display in the right panel.

New features:
- Extract basic metadata (filename, format, resolution, file size, color type)
- Parse EXIF data (camera, date, exposure, aperture, ISO, focal length, GPS)
- Display metadata in collapsible right panel (toggle with 'i' key)
- Auto-refresh metadata on document navigation

Changes by file:

Cargo.toml, Cargo.lock:
- Add kamadak-exif dependency for EXIF parsing

i18n/en/noctua.ftl:
- Add translation strings for all metadata labels

src/app/document/meta.rs:
- New module for metadata types (BasicMeta, ExifMeta, DocumentMeta)
- Extraction logic with EXIF parsing via kamadak-exif
- Helper methods for formatted display (resolution, file size, camera, GPS)

src/app/document/mod.rs:
- Re-export meta module

src/app/document/{raster,vector,portable}.rs:
- Add extract_metadata() method stubs (full impl for raster)

src/app/document/file.rs:
- Reset metadata on document change

src/app/message.rs:
- Add ToggleRightPanel and RefreshMetadata messages

src/app/model.rs:
- Add metadata: Option<DocumentMeta> field
- Add show_right_panel: bool field

src/app/update.rs:
- Handle panel toggle and metadata refresh
- Auto-refresh metadata on navigation when panel visible

src/app/view/panels.rs:
- Implement right_panel() with metadata display
- Conditional sections for basic info and EXIF data

src/app/view/canvas.rs:
- Integrate right panel into layout"

src/app/update.rs

@@ -17,14 +17,26 @@ pub fn update(model: &mut AppModel, msg: AppMessage) {
         // ===== File / navigation ==========================================================
         AppMessage::OpenPath(path) => {
             document::file::open_single_file(model, &path);
+            // Refresh metadata if panel is visible.
+            if model.show_right_panel {
+                refresh_metadata(model);
+            }
         }
 
         AppMessage::NextDocument => {
             document::file::navigate_next(model);
+            // Refresh metadata if panel is visible.
+            if model.show_right_panel {
+                refresh_metadata(model);
+            }
         }
 
         AppMessage::PrevDocument => {
             document::file::navigate_prev(model);
+            // Refresh metadata if panel is visible.
+            if model.show_right_panel {
+                refresh_metadata(model);
+            }
         }
 
         // ===== Panels =====================================================================
@@ -33,6 +45,10 @@ pub fn update(model: &mut AppModel, msg: AppMessage) {
         }
         AppMessage::ToggleRightPanel => {
             model.show_right_panel = !model.show_right_panel;
+            // Load metadata lazily when panel becomes visible.
+            if model.show_right_panel && model.metadata.is_none() {
+                refresh_metadata(model);
+            }
         }
 
         // ===== View / zoom ===============================================================
@@ -102,6 +118,11 @@ pub fn update(model: &mut AppModel, msg: AppMessage) {
             }
         }
 
+        // ===== Metadata ==================================================================
+        AppMessage::RefreshMetadata => {
+            refresh_metadata(model);
+        }
+
         // ===== Error handling ============================================================
         AppMessage::ShowError(msg) => {
             model.set_error(msg);
@@ -139,3 +160,8 @@ fn current_zoom(model: &AppModel) -> f32 {
         ViewMode::Custom(z) => z,
     }
 }
+
+/// Refresh metadata from the current document.
+fn refresh_metadata(model: &mut AppModel) {
+    model.metadata = model.document.as_ref().map(|doc| doc.extract_meta());
+}