v2.65.2 — board: gate Approve works under a minimal PATH

Fix for 'Approve' / 'Approve + ▶run' → 'bd update failed'.

Root cause: when the board is launched from a GUI / login shell whose PATH omits /opt/homebrew/bin (where Homebrew's bd lives), spawnSync('bd') returns ENOENT. bd list was served from cache so tasks still showed — masking the cause.

• The board now resolves bd once against /opt/homebrew/bin · /usr/local/bin · ~/.local/bin (override via GREAT_CTO_BD_BIN) and spawns every bd call with an augmented PATH (so bd's own git subprocess resolves too).
• Failures now return an actionable message instead of the bare 'bd update failed' (ENOENT → install Beads / set GREAT_CTO_BD_BIN; timeout → stale .beads/.lock).

Verified: a board launched with PATH=/usr/bin:/bin approves a gate (open→CLOSED) fine. No regression: board-gate 5/5, lib 348/348.