fix(render): draw the pneumatic hatch from HATCH_ARM and drop Port.side

[Alpha9463]

Summary

Resolves the last two of the nine dead declarations #304 lists.

• HATCH_ARM: it named the pneumatic hatch stroke's reach, but neither backend read it. The SVG renderer drew the strokes from bare numbers, and the draw.io exporter hard-coded an angle and length while citing HATCH_ARM as their source. Both now take the stroke from it.
• Port.side: never passed and never read; it is removed.

No drawing changes.

Related Issues

Closes #304

The other seven names were removed earlier:

• Pin.is_fixed_xy, Pin.has_grid, Route.lane, _CHAR_W and _LINE_H in b838106;
• X_GAP and Y_GAP in c45fcc0 (feat(layout): place a unit from the faces its nozzles are fixed to (#431) #442), where the column gap became the named COL_GAP.

Changes

• pandid/render/svg.py: the pneumatic hatch strokes are built from HATCH_ARM (half-reach along and across the run) instead of the literals 3 and 5. HATCH_ARM has its own doc comment.
• pandid/render/drawio.py: _HATCH_ANGLE and _HATCH_LEN are derived from HATCH_ARM using atan2 and hypot, and rounded to two places, so they come out as the same -59.04 and 11.66.
• pandid/ports.py and pandid/units.py: remove Port.side and the unused side parameter of Unit._add_port.
• tests/test_drawio.py:
  • one test checks that the SVG hatch follows HATCH_ARM; it fails on main;
  • one checks that the draw.io hatch strokes have the SVG strokes' angle and length;
  • the existing pneumatic test now shares their sheet-building helper.
• CHANGELOG.md: a "Changed" entry for the hatch and a "Removed" entry for Port.side.

API note: Port is exported, and side is removed without a deprecation release, as b838106 did for the earlier names. Code that read port.side (always None) or built a Port with side= will break. Nothing in the package, examples, docs or scripts does either.

How to Test

python3 -m pytest -q tests/test_drawio.py -k "hatch or pneumatic"
python3 -m pytest -q
python3 -m ruff check .
python3 -m ruff format --check tests
python3 -m mypy pandid
python3 -m pyright pandid

Evidence

• Renders unchanged: all 21 examples give byte-identical SVG and draw.io output to main. Eight of them draw pneumatic hatches: 04, 08, 11, 14, 15, 17, 18 and 20.
• Layout unchanged: frames, routes and validation findings are identical to main for 46 drawings (the 21 examples as authored and with placement stripped, plus four benchmark sheets).
• Full suite: 11,570 passed, 188 skipped (Python 3.14).
• Lint and types:
  • ruff, test formatting, mypy and git diff --check are clean;
  • pyright reports 0 errors on pandid/ plus the existing __all__ warning;
  • tests/test_drawio.py keeps its 240 existing diagnostics (tests/ carries 1044 pyright diagnostics, so the pyright CI gate covers pandid/ only #530); none were added.

Checklist

• Base branch is main and the branch is mergeable
• Commit subjects follow Conventional Commits; tracked work links its issue
• Self-reviewed the full diff on the Files changed tab
• Relevant local checks pass; all CI jobs pass before merge
• Documentation and examples updated if behaviour changed
• Before/after drawings included if rendered output changed (no rendered output changed)
• Blocking review feedback resolved, if review was requested

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