[codex] add incident lifecycle and war-room SDK APIs

[debidong]

Summary

Adds typed SDK coverage for the incident lifecycle and incident war-room APIs that the CLI needs, instead of keeping raw HTTP adapters in flashduty-cli.

Changes

• Add incident lifecycle methods for unack, wake, remove, disable merge, comment, and add responder.
• Add incident war-room methods for create, list, detail, delete, add member, and default observers.
• Add datasource discovery for POST /datasource/im/war-room-enabled/list so callers can find the enabled war-room IM integration.
• Add focused request-body and response-decoding tests for the new SDK methods.

Validation

• /Users/bowen/.goenv/versions/1.25.1/bin/go test -count=1 ./...

Notes

This PR is a dependency for the corresponding flashduty-cli cleanup PR, which removes the CLI-local raw incident API client and consumes these SDK methods.