Backend hardening for feed, factions, formation lifecycle, and clock consistency

[Cyber-preacher]

Stabilize server behavior to match updated web expectations and eliminate
cross-surface inconsistencies observed in production-like testing.

Feed and activity fixes:

• include faction activity in chambers/factions scoped feed filtering
• improve feed item actionability and support proper frontend open/navigation flows
• normalize event timestamp handling for consistency across event producers

Formation and proposal lifecycle fixes:

• enforce stricter formation lifecycle guards around milestone and join paths
• close edge cases allowing invalid interaction after project completion/ended states
• improve proposal/formation status projection consistency for UI consumption

Faction fixes:

• harden faction workflows tied to cofounder/invitation paths
• add persistence support for cofounder invitation lifecycle via migration
• fix activity/projection behaviors impacting feed and faction surfaces

Clock/time consistency:

• remove legacy simulated-now override path and rely on universal real-time semantics
• align scheduler/config usage with real-time behavior expectations

API/DTO consistency:

• patch response projections and DTO shape details used by web pages
• improve validation and guardrail behavior for regressions found in Phase 72

Tests:

• add targeted regression coverage for feed chambers/factions behavior
• update/add tests around formation, feed actionability, and faction flows
• keep typecheck and focused test suites green after hardening changes