feat: add bump-version.sh script for version management

Automates version bumps across all version source files:
- Cargo.toml (PRIMARY - workspace.package.version)
- debian/changelog (prepend new entry)
- debian/control (update Version field)
- scripts/build-package.sh (update VERSION variable)
- frontend/package.json (update version field)
- Stale references check after bump

Usage: ./scripts/bump-version.sh <new_version> <old_version>

migrations/011_health_check_target_host.sql

@@ -0,0 +1,10 @@
+-- Add target_host_id to health checks, allowing a check on Host A
+-- to query a service on Host B's agent (for redundant services).
+-- NULL = check own host (backward compatible).
+-- FK with ON DELETE SET NULL: if target host deleted, revert to default.
+
+ALTER TABLE host_health_checks
+  ADD COLUMN target_host_id UUID REFERENCES hosts(id) ON DELETE SET NULL;
+
+CREATE INDEX idx_health_checks_target_host ON host_health_checks (target_host_id)
+  WHERE target_host_id IS NOT NULL;