chore(agents,tool): rebuild agent config, lint gates, CI, and release tooling

Rework .agents/, Claude/Codex config, CI workflows, lint gates and
lint-rule tests, and the release/changelog tooling. The 5% comment
density gate stays diff-scoped inside git hooks, where GIT_DIR outranks
the -C the gate uses to locate the repository. The tray icon generator
writes multi-size ICO files from the SVG sources into the per-platform
tray asset directories. The custom code-review subagents are gone: the
built-in /code-review never dispatched them, and the subagent model now
lives in a user-level setting outside the repository.

The Makefile, build_config.yaml and CI hand the Core and Helper builds to
the setup build hook, so the buildkit launchers go, and setup.dart
packages AppImage and rpm on arm64 with flutter_distributor pinned to the
fork tag that normalizes packaging permissions.

Changelog: skip

.pre-commit-config.yaml

@@ -6,9 +6,21 @@ repos:
         entry: dart format
         language: system
         files: \.dart$
+        stages: [pre-commit]
+      - id: comment-density
+        name: comment density
+        entry: tool/check_comment_density.sh
+        language: system
+        files: \.(dart|kt|kts|swift|go|rs|java|cpp|cc|h|hpp|gradle|ya?ml)$
+        stages: [pre-commit]
       - id: flutter-analyze
         name: flutter analyze (pre-push)
         entry: flutter analyze --no-fatal-infos
         language: system
         pass_filenames: false
         stages: [pre-push]
+      - id: commit-msg-format
+        name: conventional commit message
+        entry: tool/check_commit_msg.sh
+        language: system
+        stages: [commit-msg]