fix(path-identity): support long Windows atomic replacement paths

[mblua]

Closes #2926

On Windows, atomic_replace_existing now canonicalizes the parent of both paths and keeps the original leaf before calling ReplaceFileW, so replacement works beyond MAX_PATH (same approach as #2923).

• One file: src-tauri/src/path_identity.rs (+82/-0), new test atomic_regular_replacement_supports_long_windows_paths.
• Negative control: test fails on main (exit 101, atomic_replace_failed, inputs 327/288 UTF-16, no verbatim prefix); passes with fix.
• Plan: .ac/plans/2926-path-identity-replacefile-long-path/plan-v3 (r1), Grinch PLAN_APPROVED + user approved. Grinch PASS on implementation and proof.
• Known pre-existing local failure: verify_directory_reason_rejects_reparse_component (symlink privilege OS 1314 on the dev host), unrelated.

[mblua]

Step 9.5 delta triage: branch is behind origin/main by docs-only commits. Delta files: docs/agents/teams-and-workgroups.md, docs/concepts.md, docs/reference/cli.md. Classification: unrelated (documentation only, no overlap with src-tauri/src/path_identity.rs, no build/config/lockfile/CI change). No branch update; land via admin merge once current head CI is green.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[mblua]

CI on 0ad378f: first run failed only config::naming_migration::tests::two_scopes_cannot_lose_each_others_records (LockUnavailable, timing; naming_migration does not use path_identity). One rerun of the failed job on the same SHA passed. All checks green (13 pass, 7 skipped).