fix: correct OR ObjectService API, add Meeting.chair + Participant.nextcloudUserId, HMAC-sign mail votes

[rubenvdlinde]

Summary

Fixes 4 CRITICALs in a single PR:

• [CRITICAL] C1: Wrong OR ObjectService API used across ~10 services — entire feature surface broken (runtime-verified) #296 C1 — Replace non-existent findObject/findObjects/getObject(register:,schema:,uuid:) calls throughout all services and controllers with the real OpenRegister API: find(id:,register:,schema:) + entity->jsonSerialize() for single objects; setRegister/setSchema + findAll(['filters'=>...]) for collections. Without this fix, every runtime call to these services returns a fatal PHP error (500).
• [CRITICAL] C2: Meeting schema missing 'chair' field — chair transitions and MCP chair checks permanently broken #297 C2 — Add missing chair field (string UUID) to Meeting schema in decidesk_register.json. Bump Meeting schema version 0.3.0 → 0.4.0 and top-level register version 0.1.0 → 0.2.0.
• [CRITICAL] C3: Participant schema missing 'nextcloudUserId' — VotingService cannot resolve any participant #298 C3 — Add missing nextcloudUserId field (string login name) to Participant schema. Bump Participant schema version 0.1.0 → 0.2.0.
• [CRITICAL] C4: Email-reply vote handler trusts client-writable '_mail' array — ballot stuffing via direct OR write #299 C4 — MailReplyHandler now HMAC-signs _mail entries at ingestion time (per-round secret via hash_hmac/sha256); verifyMailHmac() with hash_equals() guards every ballot count; email votes on isSecret: true rounds are rejected with rejectReason: secret-ballot.

Additional: test stubs updated to real OR API signatures; unit test mocks updated from old fake API to find()/findAll(); PHPCS ternary violations expanded to if/else blocks; PHPMD baseline updated for pre-existing complexity debt.

Test plan

• composer check:strict passes (PHPCS zero errors, PHPStan no new errors in changed files, PHPMD baseline clean)
• All unit service tests pass (ALVMinutesServiceTest, LiveDecisionServiceTest, ActionItemAnalyticsServiceTest, MinutesGenerationServiceTest, MotionServiceTest)
• decidesk_register.json validates — Meeting has chair field, Participant has nextcloudUserId field
• VotingService, MailReplyHandler, MinutesController callable via API without 500
• Mail vote HMAC reject path: votes without valid HMAC signature are skipped
• Secret ballot rejection: isSecret rounds reject email votes with rejectReason: secret-ballot