Phase 64: complete timer reassignment and failover

[hotzenplotz5]

Scope

Completes the remaining numbered Phase 64 reassignment/failover contracts on top of merged PR #194. Phase 65 is explicitly out of scope.

Derived contract

• allow replacement only before native dispatch or after exact authoritative absence
• atomically supersede the old exclusive owner and persist the replacement plus durable evidence
• issue a new replacement assignment identity/epoch while preserving the TimerIntent
• re-evaluate current candidate generation, write authority, capability, health, channel and conflict evidence
• fail closed for stale assignment/set/binding/operation/provider evidence
• keep dispatching, executed_unverified and outcome_unknown reconciliation-only
• preserve explicit replicas as the only intentional simultaneous owners

Safety boundaries

• preserve generation, ownership, provider, assignment, binding and fingerprint fences
• preserve no-blind-retry and outcome_unknown
• keep public SuiteBridge SVDRP help closed for NTCREATE, NTMOD and NTDELETE
• no broad Timer UI, streaming or SearchTimer redesign

Validation

• focused reassignment/failover regression
• repository atomicity/concurrency regression
• architecture/security guards
• full GitHub CI
• final real yaVDR acceptance on one exact candidate commit (separate bundled user run)

Draft remains unmerged until explicit user approval.