Suggest object overrides in map files

[ViTeXFTW]

Summary

1. Suggest indexed objects while completing top-level Object names in map.ini and solo.ini
2. Keep new object names valid by treating this as completion-only
3. Add regression coverage for blank and partial Object headers

• Closes [Feature] Show existing objects in map.ini #64

Tests

• cargo test -p zerosyntax-analysis

[greptile-apps]

Greptile Summary

This PR adds indexed base-object suggestions when completing top-level Object headers in map.ini and solo.ini while preserving support for new object names.

• Introduces a dedicated completion context for Object headers in override-layer files.
• Filters suggestions to objects with at least one non-override definition.
• Adds regression coverage for blank and partial headers and override-only objects.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
crates/analysis/src/completion.rs	Adds map/solo Object-name completion and regression tests; the previously reported override-only suggestion issue is now addressed.
crates/analysis/src/index.rs	Adds filtering that exposes only Object names backed by at least one non-override definition.

_{Reviews (2): Last reviewed commit: "fix: exclude map-only object completion ..." | Re-trigger Greptile}

[ViTeXFTW]

@greptile review