feat(profiles): snapshot pre-apply state and expose an undo for global applies

[barbatdev]

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Problem or opportunity

A successful global profile apply is irreversible. runProfilesPanelAction writes models.json with a plain write (no backup, no atomic rename), replaces materialized routing for every omitted agent, and the existing revertClaim compensation only runs on failure. Nothing snapshots the pre-apply state, so an operator who approves a dialog without fully parsing it loses the previous routing with no recovery path from the tool (manual export/restore via /gentle:models x/r is the only workaround). This is the general form of #1349: the confirmation mitigates it, but a mistake after confirming is still unrecoverable.

Proposed outcome

Before a successful apply, snapshot the pre-apply state (global routing, materialized routing, and the active-profile marker, similar to what revertClaim already knows how to restore) and expose an undo path from the profiles panel (for example, a revert action or notification-anchored undo for the most recent apply). The apply notification could then honestly claim reversibility.

Alternatives considered

• Only strengthening the confirmation dialogs (done in PR fix(profiles): require confirmation before applying an empty profile (#1349) #1384): reduces but does not eliminate unrecoverable mistakes.
• Writing pre-apply backups next to the config files on every apply, without a UI undo: cheap and already half-established by the store's .bak files, but leaves discovery to the operator.

Additional context

Raised by @jonathanludena in #1349 ("A successful apply is irreversible"); PR #1384 confirmations and follow-ups address the pre-approval side. Related: #1349, #1384, #1557.