feat: add clipboard history for code snippets

Implements issue #25 - Clipboard History feature that tracks copied
code snippets with language detection, search, and filtering.

Backend (Rust):
- New clipboard.rs module with persistent storage via tauri-plugin-store
- Commands: capture, list, delete, toggle pin, clear, search, update language
- Auto-deduplication and max history size (100 entries)
- Pinned entries stay at top and persist through clear

Frontend (Svelte/TypeScript):
- Clipboard store with filtering, search, and language detection
- ClipboardHistoryPanel component with search, language filter, pin/delete
- Clipboard button added to InputBar next to Snippets/Actions
- Auto-capture from code block copy buttons
- Auto-capture from manual text selection in terminal
- Insert snippets directly into input field

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -1,5 +1,6 @@
 mod achievements;
 mod bridge_manager;
+mod clipboard;
 mod commands;
 mod config;
 mod git;
@@ -17,6 +18,7 @@ mod wsl_bridge;
 mod wsl_notifications;
 
 use bridge_manager::create_shared_bridge_manager;
+use clipboard::*;
 use commands::load_saved_achievements;
 use commands::*;
 use git::*;
@@ -140,6 +142,14 @@ pub fn run() {
             git_log,
             git_discard,
             git_create_branch,
+            list_clipboard_entries,
+            capture_clipboard,
+            delete_clipboard_entry,
+            toggle_pin_clipboard_entry,
+            clear_clipboard_history,
+            search_clipboard_entries,
+            get_clipboard_languages,
+            update_clipboard_language,
         ])
         .run(tauri::generate_context!())
         .expect("error while running tauri application");