feat: add language synonym mapping and canonicalization

Add LANGUAGE_SYNONYMS dictionary to map language aliases to canonical IDs,
_canonical_language_id() to normalize language identifiers, and
_language_guidance() to provide language-specific instructions for LLM
code generation. This improves language detection and ensures consistent
prompt context across different language format variations.

src/utils/api.js

@@ -60,7 +60,17 @@ async function getClientIP() {
     }
 }
 
-export async function fetchSuggestion(prefix, suffix, signal, apiUrl = API_URL) {
+export async function fetchSuggestion(prefix, suffix, languageId, signal, apiUrl = API_URL) {
+    let normalizedLanguageId = 'markdown'
+    if (typeof languageId === 'string' && languageId.trim()) {
+        normalizedLanguageId = languageId.trim()
+    } else if (languageId && typeof languageId === 'object' && 'aborted' in languageId) {
+        signal = languageId
+    }
+    if (typeof signal === 'string') {
+        apiUrl = signal
+        signal = undefined
+    }
     const requestId = generateRequestId()
     const cancelUrl = getCancelUrl(apiUrl)
 
@@ -94,7 +104,7 @@ export async function fetchSuggestion(prefix, suffix, signal, apiUrl = API_URL)
         const body = {
             prefix,
             suffix,
-            languageId: 'markdown',
+            languageId: normalizedLanguageId,
             model_thinking: settings.modelThinking,
             privacy_mode: settings.privacyMode,
             user_preferences: {