feat: implement comprehensive retry mechanism and improve observability

Add retry tracking to scrape jobs with configurable max retries (default 5), implement
automatic database migrations on startup, and significantly reduce logging noise from
infrastructure layers. Enhanced tracing with structured spans for better debugging while
keeping output readable by suppressing verbose trace logs from rate limiters and session
management. Improved error handling with detailed retry context and proper session cookie
validation.

src/data/models.rs

@@ -72,4 +72,8 @@ pub struct ScrapeJob {
     pub execute_at: DateTime<Utc>,
     pub created_at: DateTime<Utc>,
     pub locked_at: Option<DateTime<Utc>>,
+    /// Number of retry attempts for this job (non-negative, enforced by CHECK constraint)
+    pub retry_count: i32,
+    /// Maximum number of retry attempts allowed (non-negative, enforced by CHECK constraint)
+    pub max_retries: i32,
 }