feat: Add hunspell dictionary support to gazetteer

Integrates the `spellbook` crate to allow for a Hunspell dictionary to
be used as a veto mechanism within the gazetteer.

This prevents common German words from being incorrectly rewritten to
vocabulary entries if they fall within the edit distance threshold. For
example, "Kaktus" will no longer be rewritten to "Lantus" if a Hunspell
dictionary is provided and contains "Kaktus".

The `hunspell_dict_path` configuration option is added, defaulting to
`/usr/share/hunspell/de_DE`. This path should point to the stem of the
Hunspell dictionary files (e.g., `/usr/share/hunspell/de_DE.aff` and
`/usr/share/hunspell/de_DE.dic`).

The gazetteer now supports an optional `DictChecker` trait, allowing for
pluggable dictionary implementations. `SpellbookDict` is the initial
implementation using the `spellbook` crate.

Includes new tests to verify the dict veto functionality, including
handling of case sensitivity and exact matches. An ignored test is added
for live verification against system-installed Hunspell dictionaries.

server/src/main.rs

@@ -10,7 +10,7 @@ use tracing_subscriber::EnvFilter;
 
 use doctate_server::analyze;
 use doctate_server::config::Config;
-use doctate_server::gazetteer::Gazetteer;
+use doctate_server::gazetteer::{Gazetteer, SpellbookDict};
 use doctate_server::transcribe;
 use doctate_server::AppState;
 
@@ -69,7 +69,7 @@ async fn main() {
     // every AI output (Whisper, oneliner, analyze). Missing / unreadable
     // vocab directory is non-fatal — the pipeline runs without
     // normalization.
-    let vocab = Arc::new(match Gazetteer::load_dir(&config.vocab_dir).await {
+    let base_gazetteer = match Gazetteer::load_dir(&config.vocab_dir).await {
         Ok(g) => {
             info!(
                 dir = %config.vocab_dir.display(),
@@ -86,6 +86,28 @@ async fn main() {
             );
             Gazetteer::empty()
         }
+    };
+
+    // Dict-veto: preserve tokens that are real German words, even if
+    // they sit at DL ≤ 2 from a vocab entry (e.g. `Kaktus` stays
+    // `Kaktus`, does not become `Lantus`). Missing / unreadable
+    // hunspell files are non-fatal — pipeline runs without the veto.
+    let vocab = Arc::new(match SpellbookDict::load(&config.hunspell_dict_path) {
+        Ok(dict) => {
+            info!(
+                stem = %config.hunspell_dict_path.display(),
+                "Hunspell dict loaded for gazetteer veto"
+            );
+            base_gazetteer.with_dict(Box::new(dict))
+        }
+        Err(e) => {
+            warn!(
+                stem = %config.hunspell_dict_path.display(),
+                error = %e,
+                "Hunspell dict unavailable; gazetteer running without dict veto"
+            );
+            base_gazetteer
+        }
     });
 
     // Transcription pipeline: channel + worker + recovery scan.