[MegaManSec]

Brings the README and the screenshot-legend script in line with the UI after #138 and #139. Every change was checked against the current code.

• Peripherals tab, not "Peripheral tab" (heading, alt texts, captions, script comments).
• Peripherals are registered with the + button under Available Peripherals, not ticked; registered rows have Send/Take buttons, which the README didn't mention.
• Open at Login, not "Launch at Login"; Take Peripherals When a Display Connects and Keyboard Shortcuts in the UI's casing.
• The menu opens on either mouse button, so "right-click" is now just "click" (the Usage table already said "either button").
• Menu-bar icon: an arrow replaces the icon while a transfer runs (it doesn't "flash briefly"), and the bell flash on an incoming ping is mentioned.
• Sync's disabled states: offline, unpaired, or nothing registered yet, with a hover reason.
• The Peripherals tab also shows errors inline, alongside Macs and Pairing.
• Screenshot legend: "Send" instead of "Release", "Open at Login".

Not changed: the PNGs in docs/assets/. Their baked-in legends still say "Release" and "Launch at Login", and the Settings window shows the old tab name; they need recapturing (the raw captures aren't in the repo).

[github-actions]

🎉 This PR is included in version 2.29.0 🎉

The release is available on GitHub release

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