Add pod-owner ELI5 of the wedge bug (wedge-explained.md)

Plain-language explanation of the reply-latch wedge for non-technical
pod owners, linked from the firmware README top. Frames the bug as a
'busy' sticky note the board forgets to take down on the give-up path,
and how RIO 4.3 fixes it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

wedge-explained.md

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+# Why your pod's stick sometimes "died" mid-battle — and why it won't anymore
+
+*A plain-language explanation for pod owners. The technical write-up is in
+[RIOv4_2-ANALYSIS.md](RIOv4_2-ANALYSIS.md).*
+
+Inside every pod is a small computer board from 1994 (the **RIO**) whose job
+is to tell the game what you're doing: which buttons you pressed, and where
+you've moved the stick, throttle, and pedals.
+
+The board and the game talk like two people on walkie-talkies. Every time the
+board reports your stick position, it waits for the game to answer *"got it."*
+During calm flying that works fine. But in a frantic firefight — lamps
+flashing, buttons hammering — the channel gets crowded, and once in a while
+that little *"got it"* gets drowned out.
+
+When that happens, the board repeats itself a few times and then, sensibly,
+gives up and moves on. Here's the bug: while it's sending a position report,
+the board puts up a mental sticky note that says *"busy — already sending
+one."* When a report goes through normally, it takes the note down. But on the
+give-up path, the 1994 programmers forgot one line — **the note never comes
+down.** From that moment the board looks at the sticky note, decides it's still
+busy, and quietly throws away every stick and throttle update forever after.
+
+That's the "wedge" you may have felt: mid-mission, your stick and throttle
+just stop doing anything, while the buttons and lamps still work fine —
+because those travel a different path that the sticky note doesn't block.
+Starting a new mission always cured it, since a new game tells the board to
+clean house, sticky note included.
+
+The **RIO 4.3** firmware adds the one missing instruction: whenever the board
+gives up on a report, it now takes the sticky note down too. We stress-tested
+it by mashing buttons at over nine presses *per second* for two minutes
+straight — the old board wedged under that abuse; the new one never misses a
+beat.