[codex] harden Discord test coverage and smoke readiness

[havlli]

Summary

• Harden signup interaction tests across every EventSignupResult.Outcome, including message edits for successful roster changes and ephemeral replies for blocked states.
• Expand scheduler coverage for repeated ticks, reminder lead time passthrough, transient error handling, and start/stop lifecycle behavior.
• Add slash-command resource contract coverage for expected command registration, organizer permissions, and key option contracts.
• Stabilize repository integration tests around database transaction time and add a local live-smoke preflight script plus docs update.

Verification

• mise exec -- mvn -ntp -Dmaven.repo.local=.m2/repository -Dtest=EventSignupCommandTest,ScheduledTaskTest,GlobalCommandRegistrarTest test
• mise exec -- mvn -ntp -Dmaven.repo.local=.m2/repository test
• mise exec -- mvn -ntp -Dmaven.repo.local=.m2/repository -Dtest=NoUnitTests -Dsurefire.failIfNoSpecifiedTests=false -Dit.test=EventRepositoryIT verify
• mise exec -- mvn -ntp -Dmaven.repo.local=.m2/repository verify
• bash -n scripts/live-smoke-preflight.sh
• scripts/live-smoke-preflight.sh expected local failure because .env is absent; Docker was reachable, .env remained ignored/untracked, and no secret values were printed.

Notes

Live Discord smoke testing remains manual and blocked until a local .env, bot token, and test server are ready.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.6%. Comparing base (736d0fe) to head (b505a8e).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #30     +/-   ##
=========================================
+ Coverage     98.0%   98.6%   +0.6%     
- Complexity    1043    1055     +12     
=========================================
  Files          116     116             
  Lines         2689    2689             
  Branches       102     102             
=========================================
+ Hits          2633    2649     +16     
+ Misses          56      40     -16     

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