feat: implement real-time CLI progress bar

[Raxyl00]

This PR implements a real-time progress bar for the CLI client (httrack) under verbose mode (-%v1).

Changes

• Implemented print_progress_bar as a private static helper in src/httrack.c.
• Displays completion percentage, visual bar [=====> ], link counters, download speed (KB/s), and calculated ETA.
• Added instant redrawing on link count updates to avoid any lag or flickering.
• Configured file completion logs in src/htsback.c and src/htsparse.c to end with \n instead of \r. This is a deliberate change to allow normal terminal scrollback for completed logs while keeping the progress bar cleanly positioned at the bottom of the screen.
• Complies with C89 formatting and uses safe string APIs (snprintf and strcpybuff).
• Uses standard ASCII symbols only (DL: instead of non-ASCII down-arrows) to ensure cross-platform terminal compatibility.

[xroche]

Thanks for this, nice idea, and the \r->\n change reads cleanly. Two things need fixing before it can land:

1. Premature "100%" mid-crawl. lien_tot isn't fixed: the engine grows it as it discovers links while parsing each page. So on the first page lien_n reaches lien_tot (1==1) before any children are found, and the lien_n == lien_tot block latches finished and prints a newline. Then lien_tot grows, finished resets, and the bar restarts. You get a stray "100%" line every time the done-count momentarily catches the known-link count. Completion should come from htsshow_end (which already passes lien_tot, lien_tot), not from the per-loop equality check.
2. OOB write on negative lien_n. percent is clamped on the high side but not the low side, so a negative lien_n produces a negative filled, and bar_str[filled] = '>' writes before the array. A low clamp (or a filled >= 0 guard) fixes it.

Two smaller things: reset the statics at mirror start so a second mirror in the same process doesn't inherit a stale finished, and add a unit test driving a 1,1 then 1,N call sequence to lock down the completion logic.