feat: add insta snapshot testing for TUI components

- Add insta dev-dependency for visual regression testing
- Create lib.rs to expose modules for integration tests
- Add snapshot tests for progress_bar, topbar, library, help modal
- Add unit tests for LibraryState navigation
- Move all tests to tests/ directory (proper Rust convention)
- Make build.rs skip proto compilation when protoc unavailable
- Add docs/testing-possible-solutions.md with testing strategies

Cargo.lock

@@ -231,6 +231,17 @@ dependencies = [
  "static_assertions",
 ]
 
+[[package]]
+name = "console"
+version = "0.16.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d64e8af5551369d19cf50138de61f1c42074ab970f74e99be916646777f8fc87"
+dependencies = [
+ "encode_unicode",
+ "libc",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "crossterm"
 version = "0.28.1"
@@ -296,6 +307,12 @@ version = "1.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
 
+[[package]]
+name = "encode_unicode"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34aa73646ffb006b8f5147f3dc182bd4bcb190227ce861fc4a4844bf8e3cb2c0"
+
 [[package]]
 name = "equivalent"
 version = "1.0.2"
@@ -612,6 +629,18 @@ dependencies = [
  "rustversion",
 ]
 
+[[package]]
+name = "insta"
+version = "1.47.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7b4a6248eb93a4401ed2f37dfe8ea592d3cf05b7cf4f8efa867b6895af7e094e"
+dependencies = [
+ "console",
+ "once_cell",
+ "similar",
+ "tempfile",
+]
+
 [[package]]
 name = "instability"
 version = "0.3.12"
@@ -1179,6 +1208,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "similar"
+version = "2.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbbb5d9659141646ae647b42fe094daf6c6192d1620870b449d9557f748b2daa"
+
 [[package]]
 name = "slab"
 version = "0.4.12"
@@ -1489,6 +1524,7 @@ version = "0.1.0"
 dependencies = [
  "color-eyre",
  "crossterm",
+ "insta",
  "nix",
  "prost",
  "ratatui",