Make OSC 7 directory tracking robust to #, %, and escaped paths - #649

Problem

The shell integrations emit the raw $PWD inside a file:// URI and the Emacs side takes the parsed path verbatim. That round trip is self-consistent but fragile:

• A # in any directory component is split off as a URI fragment by url-generic-parse-url. Locally, tracking silently stalls (the file-directory-p guard rejects the truncated path); remotely, a wrong TRAMP default-directory is committed without a check.
• Percent-encoded reports from foreign emitters — vte.sh, WezTerm, fish's builtin OSC 7, nushell's native reporting (which escapes control characters) — leave literal %20 etc. in default-directory.

Fix

Adopts the kitty/ghostty two-scheme model on both sides (ghostty's shell integrations are the reference):

• bash/zsh emit kitty's kitty-shell-cwd:// scheme, which carries the path verbatim — no shell-side encoder needed, and ghostty/kitty parse it too when the remote script runs under them (previously ghostty rejected our raw-space file:// URIs outright).
• fish percent-encodes its file:// report via the string escape --style=url builtin, exactly like ghostty's fish integration.
• ghostel--update-directory takes kitty-shell-cwd:// paths as-is (substring split so newlines survive; host downcased to keep the TRAMP connection identity consistent with file:// reports) and percent-decodes file:// paths UTF-8-aware, with %0A/%0D preserved and %00 rejected. When only the raw %XX spelling names a local directory (nushell, stale integration scripts), the raw spelling wins. A URI with an unrecognized scheme is reported instead of being mistaken for a plain OSC 9;9 path.

Compatibility

• Updated ghostel still understands old raw file:// scripts (unescaped ASCII round-trips unchanged; literal-%XX names resolve locally via the raw-spelling fallback).
• Remote (TRAMP) reports of literal-%XX names need the updated scripts; an old ghostel receiving the new scheme ignores it until both sides are current.

Verification

• make -j8 all green (elisp + native + zig tests, checkdoc, package-lint).
• New tests: kitty-scheme verbatim handling (#/?/literal %20), kitty-scheme remote TRAMP construction, file:// decoding (space, UTF-8, escaped %, raw fallback, decoded-wins-when-both-exist), a bash emitter→parser end-to-end round trip for a #/%/space path, and a fish wire-format probe. Windows-incompatible fixtures are tagged posix.
• Live-verified in a sandboxed Emacs: bash, zsh, fish, and nushell each tracked a#b?c, literal 50%20off, and päth directories correctly, with raw OSC 7 wire captures confirming the emitted forms.