v0.3.0 — Routing, placement scoring and a failure review before each order

Routing, placement scoring and a failure review before each order.

Added

• pcbkit.route, a maze router for project scripts. complete_nets joins each net's copper islands with A*
  across the copper layers, with plane and escape vias, neck-down onto small pins, GND stitching, snapping route
  ends to pad centres and an audit of every track end. Pads are obstacles by their real shape on each layer they
  reach, including pads at an angle and padstacks that differ by layer. CONN_SECONDS and DEADLINE cap the
  time per connection and per call. Harvested from the message sign, the spotlight and Orbitchron.
• pcbkit cleanup --dangling removes the dead ends a route leaves, one leaf at a time, so no net is split.
• pcbkit place-score and the placement-study skill. Score a placement by its ratsnest (crossings where two
  nets could meet on one layer, length, area over zones to keep clear, free pin and gate choices), search groups of
  parts through their candidate positions, and draw the ratsnest with the crossings circled.
• The failure-review skill. Before an order: each block against its datasheets and reference designs, the
  failure modes and how to diagnose them, test points and rework provisions, and a briefing for the user before
  any change. checklist.md lists what to check per kind of block.
• "head" on a mounting hole in enclosure.json adds a courtyard ring and an F.Cu keep-out under the screw head.
• pcbkit panel --hide-refs REGEX leaves matching references off the printable panel PDF (with --previews),
  as pcbkit previews already did.
• Releases. This changelog, scripts/release.py (bump, check, tag) and a workflow that publishes a GitHub
  release when a v* tag is pushed.
• A Claude Code marketplace. .claude-plugin/marketplace.json makes the repo installable with
  claude plugin marketplace add somebox/pcb-kit and claude plugin install pcb-kit@pcb-kit.

Changed

• pcbkit import-easyeda converts every sheet and turns EasyEDA net labels into global labels; before, only
  the first sheet came across and nets joined by label were split. The footprint saved into the library is picked
  from a stable placement, so a rerun writes the same files.
• The order checks in CONVENTIONS start with a failure review, and the PRODUCTION template has a Bring-up section.
• The README has sections on the router and the one-page design overview, and the fit-check photo.