Add regex filtering support (Fixes #554)

[sabbellasri]

Added --text, --regex, --smart
Regex filtering path in View::filter
Interactive regex edit in watch mode (/, Enter, Esc)
regex moved to top-level dependencies for cross-platform build compatibility.

[sabbellasri]

Hi @dalance Following are the changes

Added new CLI search mode flags in opt.rs: --text, --regex, and --smart (mutually exclusive).

Kept existing text/numeric search logic unchanged, and added a separate regex path in view.rs so regex is only used when regex mode is active.

Added smart regex detection in util.rs (has_regex_syntax) to auto-switch behavior in --smart mode when regex-like symbols are present.

Added argument validation in main.rs:

--regex accepts only one pattern argument.
--smart also enforces single-pattern usage when regex syntax is detected.
Added interactive regex editing in watch mode in watcher.rs: press / to edit filter, Enter to apply, Esc to cancel, backspace support, and regex error display in header.

Updated dependency placement in Cargo.toml: moved regex to top-level [dependencies] so builds work on macOS/Linux/Windows (not only Linux/Android).

The CI checks appear to be waiting for workflow approval.
Could a maintainer please approve the workflow so the builds can run?

Thank you!

[sabbellasri]

Hi @dalance, rebased on the latest upstream/master and pushed the updated branch. CI is green now, and the earlier FreeBSD failure appears to have been transient; the 3rd rerun passed. Ready for re-review.

[dalance]

Thank you for your contribution!
This PR looks good.
I have a comment about magic numbers related with ASCII code (e.g. 10, 13, ...).
It may be better that there are some comments about them.

[sabbellasri]

Hi @dalance, I replaced the raw ASCII key codes in watch mode with named constants for Enter, Esc, and Backspace/Delete in watcher.rs. Behavior is unchanged, but the code should be clearer now. If this looks good, I can merge this update into the PR.

[dalance]

I can't see your file? but it probably no problem. Please update the PR.