refactor(server): extract Cli and introspection helpers from main.rs

[vieiralucas]

Summary

• Extract the Cli struct (clap parser) from crates/fakecloud-server/src/main.rs into a new crates/fakecloud-server/src/cli.rs.
• Add a small Cli::endpoint_url() method that derives the public URL from the configured bind address (rewriting wildcard hosts 0.0.0.0 / [::] to localhost so the URL is meaningful when handed back to clients). main.rs no longer needs to do this string surgery inline.
• Extract the four introspection response builders (rds_instance_response, elasticache_cluster_response, elasticache_replication_group_response, elasticache_serverless_cache_response) into a new crates/fakecloud-server/src/introspection.rs. These translate raw service state into the public SDK types and exist explicitly so the GET /_fakecloud/... endpoints don't leak runtime-internal fields like RDS master passwords.
• The existing rds_instance_response_omits_password_but_keeps_runtime_metadata test moves with the helper.
• main.rs shrinks by 165 lines and now contains only the bind / orchestration / shutdown logic.

Test plan

• cargo fmt
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace --exclude fakecloud-e2e --exclude fakecloud-conformance
• cargo build -p fakecloud

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Summary by cubic

Split server startup by moving the CLI parser and introspection builders out of main.rs, keeping startup orchestration focused. Added Cli::endpoint_url() to derive a client-facing URL (rewrites 0.0.0.0/[::] to localhost).

• Refactors
  • New crates/fakecloud-server/src/cli.rs: defines Cli (via clap) and endpoint_url().
  • New crates/fakecloud-server/src/introspection.rs: response builders for RDS/ElastiCache map runtime state to fakecloud-sdk types without secrets; includes the password-redaction test.
  • main.rs now imports these helpers and focuses on bind/setup; reduced by ~165 lines.

^{Written for commit b32db67. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files