feat: initial Zynq XC7Z100 Flasher GUI project

Add cross-platform GUI application for programming Zynq devices
with step-by-step workflow:

- CustomTkinter GUI with dark/light theme support
- 4-step workflow: Check Env → Flash → Bootloader → Main Program
- YAML configuration with relative path resolution
- Serial monitoring and boot log parsing
- TFTP upload with CRC32 verification
- SSH/serial reboot management
- Vivado/Impact tool auto-detection

Project structure:
- app.py: Entry point
- src/: Core modules (config, flash, bitstream, tftp, serial, gui)
- config/: Default configuration template
- .flasher_env/: Python virtual environment

.gitmessage

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+# Conventional Commit Message Template
+# =====================================
+#
+# Format: <type>(<scope>): <subject>
+#
+# Type:
+#   feat:     A new feature
+#   fix:      A bug fix
+#   docs:     Documentation only changes
+#   style:    Code style changes (formatting, semicolons, etc)
+#   refactor: A code change that neither fixes a bug nor adds a feature
+#   test:     Adding or correcting tests
+#   chore:    Chores like build process, dependency updates
+#   perf:     A code change that improves performance
+#
+# Scope:
+#   The module/component affected (e.g., gui, flash, config, serial)
+#
+# Subject:
+#   A short description in present tense, imperative mood
+#   - No period at the end
+#   - Max 72 characters
+#
+# Body (optional):
+#   - Explains the "what" and "why" not the "how"
+#   - Use imperative mood
+#   - Wrap at 72 characters
+#   - Separate from subject with a blank line
+#
+# Footer (optional):
+#   - References issues (Closes #123)
+#   - Breaking changes (BREAKING CHANGE: ...)
+#
+# ── Examples ─────────────────────────────────────────────────
+#
+# feat(gui): add per-step run buttons to workflow panel
+#
+# feat(flash): implement CRC32 verification for flash programming
+#
+# fix(gui): resolve step status not updating on worker thread
+#
+# refactor(config): extract path resolution to Config.resolve_path()
+#
+# docs: update README with installation instructions
+#
+# chore: update requirements.txt with darkdetect dependency
+#
+# perf(serial): reduce serial read timeout from 10s to 5s
+#
+# ── Multi-scope changes ──────────────────────────────────────
+# Use multiple scopes when a change affects multiple modules:
+#
+# feat(gui,widgets): enhance StepHeader with run/re-run buttons
+#
+# ── Breaking changes ─────────────────────────────────────────
+# feat(gui)!: change step execution model to async
+#
+# BREAKING CHANGE: Step callbacks now receive index instead of step object