fix(cli): remove invalid 'c-S-c' key binding crashing TUI on startup

[amonkarsidhant]

Summary

• @kb.add('c-S-c') (added in 645a2f4) raises Invalid key: c-S-c from prompt_toolkit immediately after the welcome banner, making the TUI unusable on startup.
• Terminals do not deliver Ctrl+Shift+C as a key combination distinct from Ctrl+C — the shift modifier is not transmitted for control-letter sequences in standard xterm/VT encodings — so prompt_toolkit rejects the key name.
• The handler was a documented no-op anyway. Its sole purpose was preventing Hermes from intercepting native terminal copy, which already works without any binding because the terminal handles Ctrl+Shift+C before the application sees it.

Removing the binding restores TUI startup with no behavioral change to copy/paste.

Reproduction

$ hermes
... banner renders ...
Welcome to Hermes Agent! Type your message or /help for commands.
Error: Invalid key: c-S-c

Test plan

• hermes starts cleanly past the welcome banner with the patch applied
• Native terminal copy (Ctrl+Shift+C on Linux/Windows, Cmd+C on macOS) still works — was already terminal-handled
• python -m py_compile cli.py clean

[teknium1]

Duplicate — the underlying bug was fixed on main before your PR landed.

• PR #19895 by @nftpoetrist added the try/except guard (merged 2026-05-04 21:45 UTC, commit 429b8ec).
• PR #19919 followed up by removing the dead handler entirely.

Closing issue #19903 too. Thanks for jumping on it — appreciate the quick turnaround even if we only needed one of the fixes.