feat(observability): Add metrics, logging, and sync-run core modules

Introduce the foundational observability layer for the sync pipeline:

- MetricsLayer: Custom tracing subscriber layer that captures span timing
  and structured fields, materializing them into a hierarchical
  Vec<StageTiming> tree for robot-mode performance data output
- logging: Dual-layer subscriber infrastructure with configurable stderr
  verbosity (-v/-vv/-vvv) and always-on JSON file logging with daily
  rotation and configurable retention (default 30 days)
- SyncRunRecorder: Compile-time enforced lifecycle recorder for sync_runs
  table (start -> succeed|fail), with correlation IDs and aggregate counts
- LoggingConfig: New config section for log_dir, retention_days, and
  file_logging toggle
- get_log_dir(): Path helper for log directory resolution
- is_permanent_api_error(): Distinguish retryable vs permanent API failures
  (only 404 is truly permanent; 403/auth errors may be environmental)

Database changes:
- Migration 013: Add resource_events_synced_for_updated_at watermark columns
  to issues and merge_requests tables for incremental resource event sync
- Migration 014: Enrich sync_runs with run_id correlation ID, aggregate
  counts (total_items_processed, total_errors), and run_id index
- Wrap file-based migrations in savepoints for rollback safety

Dependencies: Add uuid (run_id generation), tracing-appender (file logging)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/core/config.rs

@@ -120,6 +120,41 @@ impl Default for EmbeddingConfig {
     }
 }
 
+/// Logging and observability settings.
+#[derive(Debug, Clone, Deserialize)]
+#[serde(default)]
+pub struct LoggingConfig {
+    /// Directory for log files. Default: ~/.local/share/lore/logs/
+    #[serde(rename = "logDir")]
+    pub log_dir: Option<String>,
+
+    /// Days to retain log files. Default: 30. Set to 0 to disable file logging.
+    #[serde(rename = "retentionDays", default = "default_retention_days")]
+    pub retention_days: u32,
+
+    /// Enable JSON log files. Default: true.
+    #[serde(rename = "fileLogging", default = "default_file_logging")]
+    pub file_logging: bool,
+}
+
+fn default_retention_days() -> u32 {
+    30
+}
+
+fn default_file_logging() -> bool {
+    true
+}
+
+impl Default for LoggingConfig {
+    fn default() -> Self {
+        Self {
+            log_dir: None,
+            retention_days: default_retention_days(),
+            file_logging: default_file_logging(),
+        }
+    }
+}
+
 /// Main configuration structure.
 #[derive(Debug, Clone, Deserialize)]
 pub struct Config {
@@ -134,6 +169,9 @@ pub struct Config {
 
     #[serde(default)]
     pub embedding: EmbeddingConfig,
+
+    #[serde(default)]
+    pub logging: LoggingConfig,
 }
 
 impl Config {