chore(wailsv3): add v3 Taskfile build scaffolding and config

Desktop-Linux-only scaffolding adapted from the stock v3 svelte template; no mobile taskfiles added yet.

- Taskfile.yml (root): APP_NAME AniTrack, BIN_DIR build/bin (keeps the v2 output path so release packaging is untouched), includes common+linux only, build/run/dev tasks.
- build/Taskfile.yml: stock common tasks (frontend build, bindings regen, go mod tidy).
- build/linux/Taskfile.yml: stock, minus the common:generate:icons dep (it targets macOS/Windows icons from a build/appicon.png this project does not have; icons ship via build/icon + the release tarball). Generated build/linux/AniTrack.desktop committed (stable output).
- build/config.yml: AniTrack metadata, version 1.6.8. NOTE: ./release only bumps wails.json productVersion, not this file - bump both on release until the script learns about it.
- wails.json: v3 frontend block (dir/install/build/dev/devServerUrl :5173); author + info.productVersion kept for the in-app title and the release version guard.
- Makefile: wails dev/build -> wails3 dev -port 5173 / wails3 build. The v2 webkit2_41 tag is a v2-ism v3 ignores; v3 defaults to GTK4/WebKitGTK 6.0 (same 2.52.x engine generation), so no tags.
- .gitignore: task cache dir .task/ ignored.

Makefile

@@ -1,12 +1,12 @@
-TAGS := webkit2_41
-
 .PHONY: dev build clean release
 
+# v3 uses the GTK4/WebKitGTK 6.0 stack by default (same 2.52.x engine
+# generation as the v2 webkit2_41 build), so no build tags are needed.
 dev:
-	wails dev -tags $(TAGS)
+	wails3 dev -port 5173
 
 build:
-	wails build -tags $(TAGS)
+	wails3 build
 
 clean:
 	rm -rf build/bin/*