Release v1.2.0

Promote `[Unreleased]` to `[1.2.0]` with today's date. The section
covers four user-facing features shipped on master since v1.1.1:

- CLI launch flags `--repo`, `--left`, `--right`, `--file` (#5).
- Interactive hunk overview bar (drag-to-scroll with sticky thumb,
  pixel-precise drag, click-anywhere-to-recenter, mouse-wheel
  anywhere over the bar; jump-on-mouse-up so drags can start on a
  hunk marker without stealing the jump).
- Language-aware syntax highlighting for TypeScript, YAML, Go, Rust,
  Ruby, Bash / shell, and TOML.
- Image diff for PNG / JPEG / GIF / BMP / ICO files with side-by-side,
  swipe, and onion-skin viewing modes (#9 + #16).

Minor bump per AGENTS.md §12 because the set is feature-led.

AI-Local-Session: 57980504-219e-4635-b420-38b328af9e61
AI-Cloud-Session: 46e3fd4c-04e1-4362-891d-c97594821d9d
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: geevensingh

CHANGELOG.md

@@ -12,6 +12,8 @@ body. Keep section headings exact and write notes in Markdown.
 
 ## [Unreleased]
 
+## [1.2.0] - 2026-05-19
+
 ### Added
 
 - **Command-line flags for direct launch**: `DiffViewer.exe --repo