feat: sqlite persistence with goose migrations, flashcard schema, zap logger

- Add SQLite as authoritative store alongside Qdrant (best-effort indexing)
- Use goose for embedded SQL migrations
- Schema matches flashcard format: id(INTEGER PK), note, repos, host, tags, user, context, created
- Replace std log with zap structured logger
- Split registerTools into registerStoreKnowledge + registerSearchKnowledge
- Qdrant index uses SQLite rowid directly as point ID (no SHA256 hash)
- Search enriches Qdrant results from SQLite by ID
- Lowercase auth header before prefix check
- Always handle json.MarshalIndent errors
- NixOS: StateDirectory, sqlitePath to /var/lib/st-pierre/st-pierre.sqlite

flake.nix

@@ -98,6 +98,12 @@
               default = null;
               description = "MCP Bearer token directly. Prefer tokenFile for secrets.";
             };
+
+            sqlitePath = lib.mkOption {
+              type = lib.types.path;
+              default = "/var/lib/st-pierre/st-pierre.sqlite";
+              description = "Path to the SQLite database file.";
+            };
           };
 
           config = lib.mkIf cfg.enable {
@@ -119,6 +125,7 @@
                 Group = "st-pierre";
                 Restart = "always";
                 WorkingDirectory = "/var/lib/st-pierre";
+                StateDirectory = "st-pierre";
                 ExecStart = "${st-pierre-pkg}/bin/st-pierre";
                 EnvironmentFile = lib.optional (cfg.openaiApiKeyFile != null) cfg.openaiApiKeyFile
                   ++ lib.optional (cfg.tokenFile != null) cfg.tokenFile
@@ -133,6 +140,7 @@
                   QDRANT_TLS = if cfg.qdrantTls then "true" else "false";
                   EMBEDDING_BASE_URL = cfg.embeddingBaseUrl;
                   EMBEDDING_MODEL = cfg.embeddingModel;
+                  SQLITE_PATH = builtins.toString cfg.sqlitePath;
                 }
                 // lib.optionalAttrs (cfg.openaiApiKey != null) {
                   OPENAI_API_KEY = cfg.openaiApiKey;