feat: improve browser lookup and workspace navigation

[iperev]

Summary

• Search the complete admitted requirement cohort before bounded paging; preserve exact source anchors, intersections and omission counts.
• Add lazy specification navigation and responsive Browse/Inspector panels with keyboard focus and source-bound Unicode selection.
• Preserve exact Retry operands and distinguish correction, denied, stale, unavailable and retryable failures. Late responses cannot restore request authority or enable a pending handoff.
• Declare the compatible 0.11.0 to 0.12.0 release edge without changing existing CLI wire contracts.

Verification

Final committed head: f59a964.

• Pinned npm 12.0.2: complete npm run check passed on the clean committed source.
• Browser: 228/228 passed across Chromium, Firefox and WebKit, without retries.
• Self-hosting: 104/104 requirements bound, 344 scenarios, 91 commands.
• Independent architecture, authority, decomposition, oracle and governance review found no remaining confirmed defect in the changed scope. A separate two-reviewer capture check bound six new PNGs to all 115 source inputs and reproduced the same server binary.
• Causal negative controls cover paging capacity, exact retry identity, authority-lock completion orders, pending handoff and non-cooperative late responses.

Boundaries

Browser projections remain local presentation, not proof, source editing, agent execution or merge authority. Visual evidence covers named fixture/viewport states, not all possible renderings. Review records do not establish host-enforced reviewer isolation or universal absence of defects. Registry publication is separate and has not yet occurred. Richer coverage/graph views, handoff export and the remaining roadmap are outside this PR.

Design and implementation planning records remain outside the repository.