refactor: organize source hierarchy and prepare v0.1.15

[whackur]

Group crowded frontend directories by feature and Rust TUI app modules by Git-view and navigation responsibilities. Move colocated tests, update import/mock/asset references, and refresh scoped agent guidance and architecture links. Runtime behavior, wire contracts, visibility and lazy-loading boundaries are preserved; the rebuilt viewer bundle is byte-identical.

Prepare v0.1.15 in a separate atomic commit using the release tool, with matching Rust host/plugin and viewer package versions. This branch also includes the existing four commits that remove repository-specific skills and simplify shared guidance.

Make the daemon disconnect fixture wait for attach to complete before closing its peer, so the test observes reader EOF without racing handshake timeout setup.

Verification:

• Independent review of the relocated source, facade visibility, lazy imports and test mock paths.
• Windows and Linux: workspace build, tests, rustfmt and strict all-targets/all-features clippy passed.
• Viewer: 96 test files / 869 tests passed; build passed with no dist changes.
• Release automation: 14 tests passed; next-patch policy validated against official v0.1.14.
• Existing ignored Rust tests remain unchanged; macOS verification is covered by PR CI.