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 implying 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 and creates no tracked-app state

This progresses #3 but does not close it.

Validation

• focused project-store and history tests passed
• full OpenASO suite passed: 553 tests (557 parameterized test invocations)
• project-file lint and whitespace checks passed