MuseHub v0.2.0-nightly.3

Third nightly build, version-synced with muse. The headline fix is a systemic two-column scroll bug that affected every sidebar page in the app; three other real bugs (permission, wire-protocol, and identity-display) also landed.

What changed

• Two-column scroll layout fixed across all 11 affected pages (repo home, issues list/detail, proposal detail, explore, docs, muse-docs, blame, blob, profile). The right and left columns previously scrolled together instead of independently — root cause was body { zoom: 1.25 } breaking position: sticky and 100dvh height math. Replaced every sticky-sidebar layout with a bounded-height flex/grid pattern where each column owns its own overflow-y: auto, matching the pattern already correct on the commit-detail page. All 49 frontend tests pass; verified live in a running docker container (musehub#84).
• Proposal actions (merge, request reviewer, remove reviewer) now correctly allow write/admin collaborators, not just the literal repo owner — a permission-guard implementation in proposals.py had silently diverged from the correct, collaborator-aware guard already used in issues.py (musehub#135).
• muse push no longer silently substitutes {} for an unresolvable external delta-only parent snapshot — this was a real clone-corruption path: a child commit's snapshot would be reconstructed against an empty manifest instead of the actual parent state. Fixed with a red-first TDD test proving the corruption, then the fix (musehub#134).
• Agent identity's agent_model field now reflects the most recently used model, not the value frozen at first-ever provisioning — a stale genesis value was displayed even after an agent had long since switched models (issue #132).
• Release pruning now uses PEP 440-aware version sorting instead of plain sort -V, which didn't understand PEP 440 precedence and was deleting the newest nightly instead of the oldest. Phases 1–2 (the pruning tool + wiring into publish_muse_release.sh) are live on dev; phase 3 (live re-verification against a real deploy) is intentionally held for a manual go-ahead (issue #128).
• .museagent.md migration — same cross-repo fix as muse tonight; MuseHub's own agent config now lives in a tracked file, not the untracked .muse/ directory (issue #78).

Follow-ups filed, not blocking this nightly

• muse#84 — a muse blame false-attribution bug found while root-causing the scroll fix; not yet fixed.
• musehub#136 — investigate removing body { zoom: 1.25 } in favor of rem-based scaling; blocked on a spacing-token refactor.

How the version number got picked

Every commit's sem_ver_bump is computed structurally from an AST-level diff of changed public symbols, not typed by hand — see docs/versioning.md. This nightly's structural changes classify as PATCH.