Enhance logging and error handling in PostgreSQL functions; update API endpoints in E2E tests; add Logstash troubleshooting documentation

- Added tiered logging and error handling in various PostgreSQL functions to improve observability and error tracking.
- Updated E2E tests to reflect changes in API endpoints for fetching best watched prices.
- Introduced a comprehensive troubleshooting runbook for Logstash to assist in diagnosing common issues in the PostgreSQL observability pipeline.

Dockerfile.dev

@@ -225,14 +225,20 @@ filter {\n\
     mutate { add_tag => ["error"] }\n\
   }\n\
 \n\
-  # Redis error detection\n\
+  # Redis log parsing\n\
   if [type] == "redis" {\n\
     grok {\n\
       match => { "message" => "%%{POSINT:pid}:%%{WORD:role} %%{MONTHDAY} %%{MONTH} %%{TIME} %%{WORD:loglevel} %%{GREEDYDATA:redis_message}" }\n\
     }\n\
+\n\
+    # Tag errors (WARNING/ERROR) for Bugsink forwarding\n\
     if [loglevel] in ["WARNING", "ERROR"] {\n\
       mutate { add_tag => ["error"] }\n\
     }\n\
+    # Tag INFO-level operational events (startup, config, persistence)\n\
+    else if [loglevel] == "INFO" {\n\
+      mutate { add_tag => ["redis_operational"] }\n\
+    }\n\
   }\n\
 \n\
   # PostgreSQL function log parsing (ADR-050)\n\
@@ -265,6 +271,7 @@ filter {\n\
 }\n\
 \n\
 output {\n\
+  # Forward errors to Bugsink\n\
   if "error" in [tags] {\n\
     http {\n\
       url => "http://localhost:8000/api/store/"\n\
@@ -272,14 +279,23 @@ output {\n\
       format => "json"\n\
     }\n\
   }\n\
+\n\
+  # Store Redis operational logs (INFO level) to file\n\
+  if "redis_operational" in [tags] {\n\
+    file {\n\
+      path => "/var/log/logstash/redis-operational-%%{+YYYY-MM-dd}.log"\n\
+      codec => json_lines\n\
+    }\n\
+  }\n\
   \n\
   # Debug output (comment out in production)\n\
   stdout { codec => rubydebug }\n\
 }\n\
 ' > /etc/logstash/conf.d/bugsink.conf
 
-# Create Logstash sincedb directory
+# Create Logstash directories
 RUN mkdir -p /var/lib/logstash && chown -R logstash:logstash /var/lib/logstash
+RUN mkdir -p /var/log/logstash && chown -R logstash:logstash /var/log/logstash
 
 # ============================================================================
 # Set Working Directory