fix: rebuild dashboard before npm publish

[pitimon]

Summary

• rebuild dashboard/dist inside prepublishOnly before regenerating the pricing seed
• prevent manual npm publish from silently packaging stale dashboard assets
• add regression coverage for lifecycle ordering
• bump npm, macOS, and Windows versions in lockstep to 0.39.50

Incident

0.39.49 was published manually after the automated job lacked NPM_TOKEN. The manual path packaged a stale dashboard bundle that still embedded 0.39.48; the local LaunchAgents were rolled back to the healthy 0.39.48 baseline.

Verification

• focused npm publish workflow tests: 13/13 passed
• npm publish --dry-run: dashboard rebuilt first; 180 files packaged; 22 dashboard JS assets; embedded 0.39.50; did not embed 0.39.49
• npm run ci:local: passed
• version lockstep: passed
• OpenWiki: 0 findings
• secret scan: 0 findings
• git diff --check: passed

Fixes #174