fix(cli): restore fallback paste collapse + handle long single-line pastes (#32447)

Follow-up to #32087 after community report from @ethernet that 8000-char
single-line pastes get dumped raw into the input box.

A) Fallback regression revert
   paste_collapse_threshold_fallback default: 0 -> 5
   #32087 disabled the fallback handler by default. The fallback path
   has been always-on with line_count >= 5 since #3065 (March 2026);
   the previous shape was the salvaged contributor's design and didn't
   match pre-existing behavior for terminals without bracketed paste
   support (Windows terminals, some SSH setups). Restoring the original
   on-by-default.

B) Long single-line paste guard
   New config key: paste_collapse_char_threshold (default 2000)
   Bracketed-paste handler and fallback handler now BOTH collapse when
   line count >= line threshold OR total char length >= char threshold.
   Catches the case ethernet hit: ~8000 chars of minified JSON / log
   output on a single line dumped raw into the buffer.
   TUI mirrors the same config via uiStore.pasteCollapseChars.
   Set 0 to disable.

Defaults verified:
  paste_collapse_threshold: 5
  paste_collapse_threshold_fallback: 5
  paste_collapse_char_threshold: 2000

Tests:
  tests/hermes_cli/test_config.py: 87/87 pass
  ui-tui useConfigSync.test.ts: 34/34 pass
  ui-tui useComposerState.test.ts: 9/9 pass
  tsc: 0 new errors in touched files

hermes_cli/config.py

@@ -1905,13 +1905,25 @@ DEFAULT_CONFIG = {
     },
 
     # Paste collapse thresholds (TUI + CLI).
-    # collapse_threshold: paste collapses to a file reference when line count
-    #   exceeds this value (bracketed paste, safe: appends to existing text).
-    # collapse_threshold_fallback: same but for the fallback heuristic used
-    #   by terminals without bracketed paste support (destructive: replaces
-    #   entire buffer).  0 = disabled.
+    #
+    # paste_collapse_threshold (default 5)
+    #   Bracketed-paste handler. Pastes with this many newlines or more
+    #   collapse to a file reference. Set 0 to disable.
+    #
+    # paste_collapse_threshold_fallback (default 5)
+    #   Fallback heuristic for terminals without bracketed paste support.
+    #   Same line count test but heuristically gated by chars-added /
+    #   newlines-added to avoid false positives from normal typing.
+    #   Set 0 to disable.
+    #
+    # paste_collapse_char_threshold (default 2000)
+    #   Long single-line paste guard. Pastes whose total char length
+    #   reaches this value collapse to a file reference even if line
+    #   count is below the line threshold. Catches the "8000 chars of
+    #   minified JSON / log output on one line" case. Set 0 to disable.
     "paste_collapse_threshold": 5,
-    "paste_collapse_threshold_fallback": 0,
+    "paste_collapse_threshold_fallback": 5,
+    "paste_collapse_char_threshold": 2000,
 
 
     # Config schema version - bump this when adding new required fields