chore(cleanup): drop legacy global dictionary Tauri commands — profile_terms is canonical

Task 16 of Phase 2 Remaining. Removes the three global-dictionary Tauri
commands now that all frontend callers were migrated to the profile-scoped
equivalents in Task 15:

- list_dictionary_command
- add_dictionary_entry_command
- delete_dictionary_entry_command

Also drops the DictionaryDto and its From<DictionaryEntry> impl (dead
alongside the commands), plus the now-unused kon_storage imports
(list_dictionary, add_dictionary_entry, delete_dictionary_entry,
DictionaryEntry). The storage-layer functions and the dictionary table
itself stay until Task 17 drops them.

Codex verification point 5 cleared: zero frontend callers for the legacy
commands (or their _cmd aliases) before deletion.

cargo check -p kon: clean.
cargo test --workspace: 40 passed; pre-existing ensure_x11_on_wayland
doctest failure at src-tauri/src/lib.rs:77 unchanged.

src-tauri/src/lib.rs

@@ -283,9 +283,6 @@ pub fn run() {
             commands::transcripts::update_transcript_meta_cmd,
             commands::transcripts::delete_transcript,
             commands::transcripts::search_transcripts,
-            commands::transcripts::list_dictionary_command,
-            commands::transcripts::add_dictionary_entry_command,
-            commands::transcripts::delete_dictionary_entry_command,
             // Diagnostics (panic + error capture, manual report bundle)
             commands::diagnostics::log_frontend_error,
             commands::diagnostics::list_recent_errors_command,