feat(research): add paged project history reads

[hubab1]

Summary

• add exact, lookahead-based page reads for research projects and scoped keywords
• add generation-safe project reloads for stale-revision recovery
• add a bounded shared-query ranking-history reader with deterministic ordering
• return immutable search-result observations without claiming that a pre-live project has an app rank

Safety and semantics

• project and keyword incarnation generations are validated inside the same background-store read as history
• shared ranking evidence is reused by query key and is not cloned or owned by a project
• pagination validates bounds and integer overflow, and exposes a continuation only when a lookahead row exists
• this slice performs no provider calls, creates no tracked-app state, and does not touch the protected sidebar work

Validation

• 20 focused project-store/history tests passed
• 417 full-suite tests passed
• signed Debug build passed
• strict deep code-sign verification passed
• final independent P1/P2 review was clear

Review gate

This is a stacked draft on 33b-research-metrics-workflow. It remains manually gated with the inherited V5 persistence/provider stack. The app was not launched against the maintainer's live store.

Implementation is independent; no external co-author applies.