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"

i18n/en/noctua.ftl

@@ -37,3 +37,25 @@ scale = Scale
 ## Error messages
 error-failed-to-open = Failed to open “{ $path }”.
 error-unsupported-format = Unsupported file format.
+
+# Metadata panel
+metadata = Metadata
+file-name = File
+format = Format
+resolution = Resolution
+file-size = Size
+color-type = Color
+
+# EXIF data
+exif-data = EXIF Data
+camera = Camera
+date-taken = Date
+exposure = Exposure
+aperture = Aperture
+iso = ISO
+focal-length = Focal
+gps = GPS
+
+# States
+loading-metadata = Loading...
+no-document = No document