Improve Cassandra connection resilience and configurability

[lstruman]

• Make disable_initial_host_lookup configurable via config key; replace hardcoded constant with dbconf.GetBoolean
• Add exponential reconnection policy with configurable initial interval, max retries (default 10), and max interval
• Add socket keepalive support via configurable socket_keepalive_sec
• Upgrade host selection to TokenAwareHostPolicy wrapping DCAwareRoundRobinPolicy when local_dc is set
• Fix TLS host verification: derive EnableHostVerification from insecure_skip_verify instead of hardcoding false
• Read insecure_skip_verify once and pass to loadCassandraTLSConfig to eliminate duplicate config reads
• Add tls.server_name support for SNI override
• Raise default timeouts from 1s to 10s; align sample config
• Document all new config keys in sample_webconfig.conf for both cassandra and yugabyte blocks

[Copilot]

Pull request overview

This PR improves Cassandra/Yugabyte connection robustness and configurability by moving several previously hardcoded connection behaviors into configuration, and tightening TLS verification behavior.

Changes:

• Adds configurable connection options (timeouts, socket keepalive, disable_initial_host_lookup) and an exponential reconnection policy.
• Improves host selection when local_dc is set by switching to token-aware routing over DC-aware round-robin.
• Fixes TLS host verification behavior (driven by tls.insecure_skip_verify) and adds tls.server_name for SNI override; updates sample config accordingly.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

File	Description
db/cassandra/cassandra_client.go	Adds configurable timeouts/keepalive/reconnection policy, token-aware host selection, and corrected TLS verification/SNI handling.
config/sample_webconfig.conf	Documents new Cassandra/Yugabyte config keys and updates sample defaults (timeouts, connections, TLS server_name).
.gitignore	Adds ignore entries for .opencode/ and CLAUDE.md.

Suppressed comments (1)

config/sample_webconfig.conf:268

• Same as above: an empty tls.server_name will default to the corresponding hosts entry, which may be a DNS name, not necessarily an IP address.

                // Override SNI hostname sent during TLS handshake.
                // Required when the certificate uses DNS SANs only (no IP SANs).
                // Leave empty to use the host IP address (gocql default).
                server_name = ""

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