feat: Add --config flag for custom settings file path (#166)

* Add --config flag for custom settings file path

Allow users to specify an alternative settings file via `--config <path>`,
enabling distinct status line configs for different Claude Code instances.

- Add initConfigPath/getConfigPath/isCustomConfigPath to config.ts
- Fix backup path to always append .bak instead of replacing .json suffix
- Use path.dirname(SETTINGS_PATH) instead of CONFIG_DIR for mkdir
- Parse --config arg in ccstatusline.ts main() entry point
- Add tests for config path management

* Integrate --config flag with Claude Code install commands

When a custom config path is active, the install-to-Claude-Code feature
now appends --config <path> to the status line command. Also updates
isInstalled detection to recognize commands with the --config suffix.

- Add isKnownCommand() to deduplicate command-matching logic
- Add shell-safe path quoting for --config values with spaces/special chars
- Add buildCommand() to append --config when custom path is active
- Refactor isInstalled() to use isKnownCommand()
- Use isKnownCommand() in App.tsx install flow
- Add tests for isKnownCommand() and buildCommand() with CLAUDE_CONFIG_DIR safety net

* Show custom config path in TUI header

When a custom --config path is active, display it below the title bar
so users can see which settings file is being edited.

* fix: use platform-appropriate quoting for --config path

* chore: bump version to 2.1.8 and update recent updates

---------

Co-authored-by: Matthew Breedlove <sirmalloc@gmail.com>

README.md

@@ -46,7 +46,7 @@
 
 ## 🆕 Recent Updates
 
-### v2.1.0 - v2.1.7 - Usage widgets, links, new git insertions / deletions widgets, and reliability fixes
+### v2.1.0 - v2.1.8 - Usage widgets, links, new git insertions / deletions widgets, and reliability fixes
 
 - **🧩 New Usage widgets (v2.1.0)** - Added **Session Usage**, **Weekly Usage**, **Block Reset Timer**, and **Context Bar** widgets.
 - **📊 More accurate counts (v2.1.0)** - Usage/context widgets now use new statusline JSON metrics when available for more accurate token and context counts.
@@ -56,6 +56,7 @@
 - **➖ New Git Deletions widget (v2.1.4)** - Added a dedicated Git widget that shows only uncommitted deletions (e.g., `-10`).
 - **🧠 Context format fallback fix (v2.1.6)** - When `context_window_size` is missing, context widgets now infer 1M models from long-context labels such as `[1m]` and `1M context` in model identifiers.
 - **⏳ Weekly reset timer split (v2.1.7)** - Added a separate `Weekly Reset Timer` widget.
+- **⚙️ Custom config file flag (v2.1.8)** - Added `--config <path>` support so ccstatusline can load/save settings from a custom file location.
 
 ### v2.0.26 - v2.0.29 - Performance, git internals, and workflow improvements