Allow custom keybindings for "Copy relative path" and "Copy absolute path"

[robert-flo]

Feature request

Currently Copy relative path and Copy absolute path are only reachable via the ≡ menu — they don't have an Esc <key> shortcut like most other menu actions (Esc s, Esc f, Esc n, etc.).

Since these two actions are things I reach for constantly (mainly to paste paths into an AI coding agent or into SSH commands), having to open the menu every time breaks the "mouse-first, low friction" flow that's the whole point of SpiceEdit.

Proposed solution

Two options, either would work for me:

1. Ship default hotkeys for these two actions, the same way every other menu item already has one (e.g. Esc y for relative path, Esc Y for absolute path — just an example, happy to defer to whatever fits the existing scheme).
2. User-defined keybindings, following the same pattern already used for custom actions (~/.config/spiceedit/actions.json). A small ~/.config/spiceedit/keybindings.json (or a keybindings section reusing the same file) mapping built-in menu actions to an Esc <key> combo would let each user pick their own, without turning this into a general config file.

Given the project's stance against a general config file, option 2 (opt-in, small JSON, mirrors the existing actions.json mechanism) seems more in line with the project's philosophy than adding a new file just for this.

Screenshot for context

Attached: the ≡ menu, showing Copy relative path and Copy absolute path with no Esc shortcut next to them.