feat(sync): wire ChangeType::Delete / sync_model for tag deletion, unapply, and apply paths

Overview

Several tag mutation code paths skip cross-device sync propagation even though the sync infrastructure already supports ChangeType::Delete and sync_model. Until these are wired, peers will diverge silently: deleted/unapplied tags remain on other devices; applied tags may never be broadcast.

Raised from PR #3044 (discussion: https://github.com/spacedriveapp/spacedrive/pull/3044#discussion_r2983003277).

Affected locations

1. Tag deletion — core/src/ops/tags/delete/action.rs (line 101)

// TODO(sync): Tag deletion is not synced to other devices.
// The sync infrastructure supports ChangeType::Delete but the tag deletion
// path does not yet call library.sync_model() with it.

Call library.sync_model(..., ChangeType::Delete) after a successful delete_tag and handle / log errors.

2. Tag unapply — core/src/ops/tags/unapply/action.rs (line 110)

// TODO(sync): Tag unapply is not synced to other devices.
// The sync infrastructure supports ChangeType::Delete but tag removal
// does not yet call library.sync_model().

Call library.sync_model(..., ChangeType::Delete) for each removed user_metadata_tag row after the bulk delete and handle / log errors.

3. Tag apply (metadata manager) — core/src/ops/metadata/manager.rs (lines 530, 547, 568)

Three call sites that map the result of apply_semantic_tags silently discard the returned models instead of looking up the actual UUID and calling sync_model:

.map(|_| ()) // TODO: Look up actual UUID and sync models

These should retrieve the inserted / updated user_metadata_tag rows, then call library.sync_model(..., ChangeType::Insert) (or Update) for each.

Acceptance criteria

• tags.delete propagates the deletion to peers via sync_model with ChangeType::Delete.
• tags.unapply propagates removed tag associations to peers via sync_model with ChangeType::Delete.
• The three apply_semantic_tags call sites in metadata/manager.rs sync inserted/updated rows to peers.
• All inline TODO(sync) and // TODO: Look up actual UUID and sync models comments in the above files are removed and replaced with a reference to this issue (e.g. // tracked in #<issue>) until resolved, then removed entirely on completion.
• No new silent divergence paths are introduced for tag mutations.

Start by reading the existing sync infrastructure and the affected paths in core/src/ops/tags/delete/action.rs, core/src/ops/tags/unapply/action.rs, and core/src/ops/metadata/manager.rs. Compare nearby library.sync_model calls and trace the models returned by delete_tag, the bulk unapply, and apply_semantic_tags. Done means all listed tag mutations propagate the appropriate changes, errors are handled, and the noted TODO comments are resolved.