add vision analysis service with prompt versioning, response schema, and structured JSON output

src/db/attachments.js

@@ -14,6 +14,15 @@ export function initializeAttachments(db) {
             position INTEGER NOT NULL DEFAULT 0, PRIMARY KEY(message_id, attachment_id)
         );
         CREATE INDEX IF NOT EXISTS attachment_references ON message_attachments(attachment_id);
+        CREATE TABLE IF NOT EXISTS attachment_vision_analyses (
+            attachment_id TEXT NOT NULL REFERENCES attachments(id) ON DELETE CASCADE,
+            vision_model TEXT NOT NULL,
+            prompt_version INTEGER NOT NULL,
+            question TEXT NOT NULL,
+            analysis TEXT NOT NULL,
+            analyzed_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP,
+            PRIMARY KEY (attachment_id, vision_model, prompt_version, question)
+        );
         CREATE TABLE IF NOT EXISTS upload_deletions (storage_key TEXT PRIMARY KEY);
         CREATE TRIGGER IF NOT EXISTS release_message_attachment AFTER DELETE ON message_attachments
         BEGIN