Nightly 3 — agent-config path fix, reflog/blame fixes, snapshot-ID migration tool

Muse v0.2.0-nightly.3

Third nightly build. Two tickets closed outright, a new symmetric-key migration tool built and merged as defensive tooling, and the workspace's agent-config canonical path bug fixed at the root.

What changed

• muse reflog now prints full 64-char sha256: commit IDs in its human-readable text output instead of truncated 12-char short IDs — matching every other Muse command's convention (muse#52).
• Removed the deprecated muse migrate command and its backing domain_migration.py module entirely — the sequential-integer domain identity format it supported no longer exists anywhere in this workspace (muse#38).
• muse code fix-snapshot-ids — new CLI tool to migrate snapshot content-IDs to the unified-store scheme, built defensively while investigating musehub#134's corrupted-commit fallout. Not currently needed in production, merged to dev so the work isn't lost if the underlying corruption resurfaces (muse#83).
• Agent-config canonical source moved outside .muse/ — .muse/agent.md was never actually tracked by Muse (an internal directory, invisible to commits), which defeated the entire purpose of a trackable, cloneable agent config. The canonical file is now .museagent.md at the repo root, with auto-migration of any existing .muse/agent.md on agent-config init/sync (issue #78, phases 1–3; phase 4 workspace-wide sweep still open).
• muse hub user read/update no longer call a non-existent /profile URL suffix — this was silently broken for any agent trying to read or update a MuseHub user profile. update also now correctly sends PUT, not PATCH (issue #79).
• Git-bridge backup routine hardened: split the combined verify and github-push scripts into -muse/-musehub variants, switched to HTTPS remotes instead of SSH, fixed the GitHub repo path to use the actually authenticated gh account, made future backup repos public by default, and fixed a SIGPIPE crash in replay --limit at real backup scale.

Follow-ups filed, not blocking this nightly

• muse#84 — muse blame --range confirmed to attribute lines to a commit whose own files_modified list excludes the file, and whose blob for that file is byte-identical to its parent. Reproducible, not yet fixed.
• musehub#136 — investigate removing musehub's 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.