bug(keybinding): Ctrl+Y overrides Pi yank, /hotkeys omits 13+ shortcuts

[akougkas]

Problem

Ctrl+Y override (feature loss):
PanCode's pi.registerShortcut("ctrl+y") overrides Pi editor's yank action (kill ring paste). Users lose Emacs-style kill ring functionality. The Pi SDK's yank is a non-reserved editor action so the override succeeds with a diagnostic warning. This trade-off is not documented anywhere.

Incomplete /hotkeys display:
The /hotkeys command shows 11 shortcuts (3 PanCode + 8 Pi). The full Pi SDK has 17+ app-level bindings plus all editor bindings. Omitted shortcuts users should know about:

• ctrl+z (suspend to background)
• shift+ctrl+p (cycle model backward)
• ctrl+g (open in external editor)
• alt+up (dequeue follow-up messages)
• ctrl+v (paste image)
• shift+enter (new line in editor)
• ctrl+k (delete to line end)
• ctrl+w (delete word backward)
• Double escape (tree/fork toggle)
• ! / !! (bash command prefix)

Shift+Tab description incomplete:
/hotkeys shows "Cycle mode (Plan, Build, Review)" but does not mention that it also auto-sets reasoning level per mode (see issue #100).

Audit Reference

AUDIT-ISSUES.md: D1, D2, D8

Objective

Document all keybinding trade-offs and make the full shortcut surface discoverable.

Deliverables

• Add "Editor Shortcuts" section to /hotkeys with common editor bindings
• Add "Bash" section showing ! / !! prefix syntax
• Document Ctrl+Y yank override as a known trade-off in PAN-KEYBOARD-BINDINGS.md
• Update Shift+Tab description: "Cycle mode and reasoning (Plan/high, Build/medium, Review/xhigh)"
• Consider moving safety cycling to a different key to restore yank