v0.10.3: Compare convergence, reference persistence, scrollable body, richer preview

[divijg19]

Compare Workspace convergence:

• Add model.Result.Sequence for stable O(1) request identity (#NNN).
• Rename PinnedBaseline -> Reference across model, workspace, render and docs; RenounceReference() is the sole way to drop the cross-run reference.
• x is context-sensitive: clears the session (reference preserved) or, with only a reference, renounces it; startRun carries the reference forward.
• Comparison identity block and Raw view show request # and timestamp for both participants.
• Body/Raw compare views are scrollable with a position hint.
• Enrich the right-side preview drawer (identity, verdict, keybindings).
• Remove dead no-op Exit(); esc returns to Observe without mutation.

Polish / cleanup pass:

• Remove dead code: IsIdle, HasCandidate, stray EXECUTE orientation label, redundant payloadGeometry field, and the redundant Model.status field (tests now assert on observable state). cancelRun clears m.cancel.
• DRY: renderIdentityLine shared by comparison block and preview; header sections collapsed into one loop; shared promotedHeaderKeys set; unified timestamp formatting.
• Correctness: withScrollHint and visibleWindow clamp against short heights; verifySectionOrdering now actually runs across the three views.
• Tests: enterComparing/setComparing helpers de-duplicate setup; tighter timestamp assertion.
• Docs: drop non-existent Exit() op and ComparisonSession -> CompareWorkspace; tui/README links the COMPARE_* docs; Makefile arch gates pruned and doc-freshness checks real paths.

[divijg19]

v0.10.3: Compare convergence, reference persistence, scrollable body, richer preview