feat(desktop): support custom user data directories

[murongg]

Markra currently ignores --user-data-dir, so a portable executable still uses the system profile. This adds a startup option for keeping settings and persistent app data in a directory on a USB drive or another user-selected location.

• Accept --user-data-dir=<path> and --user-data-dir <path>; resolve relative paths against the launch working directory, create missing directories, and reject invalid or unwritable storage.
• Use the selected directory for startup preferences, settings and AI session stores, attachments, themes, templates, document history, spellcheck dictionaries, logs, and window state.
• Keep document/folder launch arguments working, reject forwarding an explicit different profile to an existing instance, and preserve the resolved directory after Windows portable updates.
• Add English/Chinese usage examples and document profile migration and platform behavior.

Closes #755.

Validation

• cargo test --lib --quiet: 313 tests passed.
• cargo fmt --all --check: passed.
• cargo build: passed on macOS.
• pnpm --filter @markra/desktop test: 178 tests passed.
• pnpm --filter @markra/desktop build: passed, including vendor chunk verification.
• pnpm --filter @markra/desktop typecheck:test: passed.
• Native macOS QA with an isolated app and synthetic data: relative and absolute directories, both parameter forms, settings writes, theme/session/log/window-state persistence, startup preference reads after restart, secondary-instance file opening, directory-conflict dialog, and malformed arguments.

Platform and migration notes

The existing system profile remains the default when the option is omitted. New directories start with independent settings; existing data is not moved automatically, and external document paths are not rewritten. Quit Markra completely before switching directories.

Windows/Linux webviews use the selected directory. macOS custom profiles use ephemeral WKWebView storage because arbitrary cache directories are unsupported; durable Markra data still uses native profile paths.

Windows/Linux native runtime QA has not been performed. The local Windows cross-compile attempt stopped before compilation because the offline cache lacked clipboard-win v5.4.1; the PR CI includes Windows test compilation and Linux/macOS tests.

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Project	Deployment	Actions	Updated
markra-web	Ready	Preview	Oct 11, 2026 9:37am UTC