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.

Taskfile.yml

@@ -0,0 +1,30 @@
+version: '3'
+
+vars:
+  APP_NAME: "AniTrack"
+  # build/bin keeps the v2 output path so the release packaging is unchanged.
+  BIN_DIR: "build/bin"
+  PACKAGE_MANAGER: '{{.PACKAGE_MANAGER | default "npm"}}'
+  VITE_PORT: '{{.WAILS_VITE_PORT | default 5173}}'
+  # Target OS for build/package/run. Defaults to the host OS.
+  GOOS: '{{.GOOS | default OS}}'
+
+includes:
+  common: ./build/Taskfile.yml
+  linux: ./build/linux/Taskfile.yml
+
+tasks:
+  build:
+    summary: Builds the application
+    cmds:
+      - task: "{{.GOOS}}:build"
+
+  run:
+    summary: Runs the application
+    cmds:
+      - task: "{{.GOOS}}:run"
+
+  dev:
+    summary: Runs the application in development mode
+    cmds:
+      - wails3 dev -config ./build/config.yml -port {{.VITE_PORT}}