Add OSC 133 imenu integration; fix line-mode scrollback navigation

[dakra]

Summary

Two related changes — the second was discovered while testing the first.

1. Stop resize redraw from re-anchoring scrollback in line mode

consult-line, consult-imenu, and any goto-char jump in line mode appeared to land on the target and then snap back to the live cursor. isearch worked because it advances window-start as it scrolls.

The minibuffer that consult opens resizes the ghostel window twice (open + close). Each resize forces a redraw with ghostel--redraw-resize-active = t. The predicate's resize branch classified a window as anchored whenever it was absent from ghostel--scroll-positions — meant to cover Emacs's own keep-point-visible drift on window-start but ignored window-point entirely. After the user navigated point into scrollback, no plain redraw ran while the minibuffer was open, so ghostel--scroll-positions stayed empty; the closing resize then re-anchored the window and yanked window-point back to the live cursor.

Fix: a window-point >= anchor guard on the resize branch. The drifted-window-start case still passes; the scrollback-jump case no longer does.

2. Add OSC 133 imenu integration

Each shell prompt with OSC 133 'A'/'B'/'C' markers becomes an imenu entry of the form <cwd> <command>, target landing on the prompt prefix's start. Composes with consult-imenu, imenu-list, evil's ]m/[m, etc.

The cwd is captured at OSC 133 'C' (command-start) and pushed onto a chronological list; reading default-directory lazily at index time would mis-attribute every prior prompt to the current cwd after a cd.

Position-based tracking (text properties or markers) does not survive: the renderer's per-row delete+reinsert wipes ad-hoc text properties on dirty rows, and eraseBuffer (resize-cols, force-full redraw, scrollback edge cases) collapses every marker to point-min. Pairing chronological cwds with the ghostel-prompt regions in buffer order at index time is robust to both: resize reflows the grid but preserves prompt order; scrollback eviction is detected as (cwd-count > region-count) and trims the oldest cwds.

Selecting an entry leaves line and copy modes untouched (the user is already free to navigate); only semi-char and char modes switch to emacs mode so point can move at all.

Test plan

• make -j4 all — 331 elisp + 138 native tests pass; lint clean
• New regression test ghostel-test-redraw-resize-preserves-scrollback-jump covers the consult-line scenario
• 15 new imenu tests cover empty buffer, single/multi prompts, cwd attribution, multi-line commands, label truncation, scrollback eviction, and the goto behaviour in each input mode
• Live verified in emacsclient: consult-line, consult-imenu, plain imenu all stick on the target line in line mode