The safe zone never refuses a move that goes no deeper than the pose the arm starts in #161

Part of #144. The real arm rests 28-34 mm "into" the virtual table, so every target was refused. Pull #151 had this; take it from branch smith/144-top-the-arm-moves-when-you-drive-it-the.

Done:

• [ ] In Software/so101/src/server.ts, checkPath (moves, park, playback approach) ignores any penetration no deeper than the start pose's. A move that goes deeper is still refused with its reason. The stream path keeps its own back-out rule, and warn mode never refuses.
• [ ] Tests (src/server.test.ts): an arm 30 mm in the table can move up, and is refused moving further down with a reason naming the link and depth.
• [ ] Branched from main at 1142ee6 or later; forge.json untouched. bun --cwd Software/so101 test passes.