fix(transport): transport template NativeAlarmSources — imports no longer amputate native alarm mirrors nor dangle instance overrides

New TemplateNativeAlarmSourceDto + init-only TemplateDto.NativeAlarmSources (empty
default, additive — IsInherited placeholders carried for the collision detector).
Exported in ToBundleContent, consumed in FromBundleContent + BuildTemplate, and a
new SyncTemplateNativeAlarmSourcesAsync runs the Overwrite add/update/delete child
sync with per-change audit rows. ArtifactDiff.CompareTemplate now DiffChildren over
native sources so Preview reports a NativeAlarmSources field change. Proven by an
end-to-end flatten test: an instance native-alarm-source override that dangled
pre-fix now resolves against the re-imported template source.

Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj

docs/requirements/Component-Transport.md

@@ -21,7 +21,7 @@ As of M8 (T18), Transport is no longer limited to central-only configuration: it
 - Move **site-scoped configuration** (T18): `Site` definitions, site-scoped `DataConnection`s (protocol connections — distinct from External-System `DatabaseConnection`s), and `Instance`s along with their `InstanceAttributeOverride` / `InstanceAlarmOverride` / `InstanceNativeAlarmSourceOverride` / `InstanceConnectionBinding` children and `Area` membership (carried by name).
 - Reconcile cross-environment site identifiers and connection names through the **name-mapping subsystem** (`BundleNameMap`): auto-match by identifier/name, operator override via the import-wizard Map step or CLI flags, and per-conflict create-or-bind resolution (see "Name Mapping").
 - Compute a **per-line (Myers) diff** for code fields on Modified artifacts (T20) via the pure `LineDiffer`, embedding a size-capped structured line diff in each `ArtifactDiff`.
-- Serialize and deserialize all transportable entity types to/from bundle DTOs, carving secret fields into an isolated `SecretsBlock`.
+- Serialize and deserialize all transportable entity types to/from bundle DTOs, carving secret fields into an isolated `SecretsBlock`. A template travels with **all** of its child collections — `TemplateAttribute`, `TemplateAlarm`, `TemplateScript`, `TemplateComposition`, and `TemplateNativeAlarmSource` (including `IsInherited` placeholder rows, which the collision detector depends on) — each field-faithful on Add and reconciled add/update/delete on Overwrite. Carrying the native alarm sources is what keeps an imported `InstanceNativeAlarmSourceOverride` from dangling against a source the target template would otherwise lack.
 - Encrypt content with AES-256-GCM + PBKDF2-SHA256 (600 000 iterations) when a passphrase is supplied; leave content plaintext with a UI warning and an `UnencryptedBundleExport` audit event when none is given.
 - Validate `manifest.json` on upload: format version gating, SHA-256 content hash verification.
 - Manage in-memory `BundleSession` objects: 30-minute TTL, 3-strike passphrase lockout per session.