feat(core): one versioning rule — every mutation snapshots and bumps version

[cuibonobo]

Summary

Closes #61.

Only content updates participated in versioning before this: associate(), dissociate(), setPermissions(), and delete() passed straight through to the adapter — no snapshot, no version bump, no audit trail. That made #59's recoverability promise ("anything a write-holder does, the owner can undo") false for every association or permission change, and left ifVersion-style conflict detection (#48) blind to non-content races.

One rule now, no special cases: every mutation of a record — content, associations, permissions, soft delete, undelete — snapshots the prior full state and bumps version. Hard delete is the one exception; it destroys the record and its history outright, so there's nothing to snapshot.

What's added

• RecordVersion gains optional associations/permissions (packages/core/src/types.ts, wire-types, adapter-api's parseVersion/serializeVersion). The SQLite adapter's versions table had no columns for either — added as JSON, the same pattern already used for permissions on the live records table.
• associate/dissociate/setPermissions/delete (soft)/undelete all fetch the record, snapshot it, mutate, then bump version — with no-op guards so an identical re-associate, a dissociate of something not present, or a deep-equal setPermissions costs nothing (no bump, no snapshot). Association equality matches the SQLite adapter's existing primary key (kind, label, fileId/recordId — mimeType excluded).
• restoreVersion() now restores associations when the target snapshot has them, but never permissions — those stay owner/creator territory (setPermissions's existing carve-out), so a content rollback can't silently widen or narrow access as a side effect.
• Behavior tightening, worth flagging: associate/dissociate/soft-delete didn't fetch the record first, so a call against a missing record either silently no-op'd or threw a generic adapter Error, depending on which adapter. Snapshotting requires fetching first, so these now consistently throw StackNotFoundError — matching update/setPermissions/undelete/restoreVersion, which already worked this way.
• Spec (docs/spec.md) states the one-rule contract in §Versions and updates the wire endpoint description to match.

Out of scope (per #61's own comment thread)

Extending the ifVersion CAS option to the newly-versioned paths — that's #48's feature and it hasn't landed at all yet (no ifVersion anywhere in the codebase to extend).

Test plan

• Added tests across packages/core (version monotonicity across mixed mutations, no-op guards, restore-restores-associations, restore-never-restores-permissions, StackNotFoundError for missing records), record-adapter-sqljs (version round-trip of associations/permissions), and adapter-api (wire parsing of the new fields)
• pnpm -r build — clean
• pnpm -r typecheck — clean across all 6 packages
• pnpm -r lint — clean
• pnpm -r test — 371 tests passing workspace-wide
• prettier --check on changed files — clean

Refs #61, #59, #48, #47

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