fix(ui): hover-panic on non-ASCII links, paste and clipboard spoofing, image budget, links

- is_web_url sliced the string at byte 7/8, panicking (and killing every
  session) when a remote host printed an OSC 8 or plain link with a
  multi-byte character at that offset and the user hovered it. It now
  compares bytes.
- Paste confirmation also triggers on control characters other than tab
  (readline's C-o runs a line with no newline), and the preview shows
  them escaped.
- Remote clipboard toasts escape control characters and state the line
  count, so 'ls\ncurl … | sh' no longer reads as a harmless 'ls'.
- Inline images: dimensions are read from the header first and anything
  over the 32 Mpx per-terminal budget is refused before decoding.
- Toasts: repeats extend the visible toast and at most 8 are kept, so
  trigger or OSC 52 floods can't stall frames.
- The URL regex is compiled once.
- Enable eframe's 'links' feature: without it every 'open in browser'
  (Cmd/Ctrl+click, GitHub repo links, the update link) was a silent
  no-op. Adds webbrowser 1.2.4 to the lockfile.

rust/app/Cargo.toml

@@ -10,7 +10,7 @@ path = "src/main.rs"
 
 [dependencies]
 nexus-core = { path = "../core" }
-eframe = { version = "0.36", default-features = false, features = ["default_fonts", "glow", "wayland", "x11", "accesskit", "persistence"] }
+eframe = { version = "0.36", default-features = false, features = ["default_fonts", "glow", "wayland", "x11", "accesskit", "persistence", "links"] }
 egui = "0.36"
 parking_lot = "0.12"
 zeroize = "1"