cleanup: `matchesIgnore` is an incomplete glob, doesn't support `**`, `!`, or `?`

[gitcoder89431]

Problem

The client-side matchesIgnore in internal/syncthing/client.go only handles three cases:

• node_modules/ (trailing slash = dir match)
• *.ext (single leading wildcard)
• Exact name matches

Syncthing's .stignore format also supports:

• ** (recursive glob)
• ? (single character wildcard)
• !pattern (negation/re-include)
• (?i)pattern (case-insensitive flag)

If a user adds docs/**/*.md or !important.txt to their .stignore, the TUI file list will show incorrect sync/hidden state for those files.

Fix

Replace the hand-rolled matching with filepath.Match for basic glob support, and handle the ! negation prefix. Document that ** and Syncthing-specific flags ((?i), (?d)) are not fully supported client-side, as full support would require reimplementing Syncthing's ignore engine.

[gitcoder89431]

Fixed in 0f8ca1d