Extend AltiumSchematicParser for DNP / MPN / pin-net mapping

[RFingAdam]

Problem

The existing Altium parser handles the basic OLE2 structure but misses Parameter records (DNP, MfrPartNum, ComponentClass), harness/sheet-symbol traversal, and pin-net resolution. Without these, the schematic-aware analyzers run in degraded mode against .SchDoc files.

Acceptance criteria

• Parse Parameter records inside Records stream → populate ParsedComponent.part_number, manufacturer, properties['component_class'], properties['dnp'].
• Sheet-symbol records walked to surface sub-sheet hierarchy.
• Pin records linked to net records via NetIdentifier → ParsedComponent.pins.
• At least one round-trip test using a minimal synthetic .SchDoc (or a mocked OLE stream).
• Backwards-compatible with existing test_altium_parser_smoke.py.

[RFingAdam]

Partially delivered by PR #125: AltiumComponent gains a properties dict; _parse_records maps Parameter rows (DNP / DONOTPLACE / NOSTUFF → properties['dnp']; COMPONENTCLASS → properties['component_class']; COMMENT/NOTE; unknown parameter names stashed under lowercase keys).

Deferred (kept open): sheet-symbol traversal + pin-net resolution. Real .SchDoc binaries are OLE2 compound documents and impractical to synthesise; the existing fixture (tests/fixtures/sample.SchDoc) is only an OLE header stub for format-detection smoke tests. Closing the remaining acceptance criteria needs at least one licensed .SchDoc sample under a permissive license.

[RFingAdam]

Closed by v0.4.1.

All five acceptance criteria met:

• AC1 — Parameter records (Add pre-compliance test plan generation #41) populate ParsedComponent.part_number, manufacturer, properties['component_class'], properties['dnp']. The logic existed before v0.4.1 but was never exercised by a test (the old test file shadowed it with a duplicate _apply_params helper); 11 of the 17 new tests now hit the real _parse_fileheader.
• AC2 — Sheet-symbol (Crystal oscillator EMI and SMPS harmonic analysis #15) + FILE_NAME (Create web UI dashboard #33) records walked. AltiumSchematicData.sheet_symbols and child_sheets populated, surfaced through the converter into ParsedSchematicData.sheet_count and properties['child_sheets'].
• AC3 — Pin records (Deep ODB++ extraction: drill data, board outline, copper pours, DRC, manufacturing notes #2) link to nets via NetIdentifier when explicit; fall back to the shared geometric resolver (WIRE + NET_LABEL coordinate snap) otherwise. ParsedComponent.pins[*]['net'] populated end-to-end.
• AC4 — 17 integration tests in tests/test_altium_parameter_records.py build synthetic FileHeader byte streams and call the production _parse_fileheader directly. No mocked OLE2 needed; synthetic-byte approach is equivalent and faster.
• AC5 — Backwards-compatible. tests/test_altium_parser_smoke.py still green; full suite at 1616 passed / 11 skipped / 0 failed.

Bonus: a hidden gap was that the dispatch returned AltiumSchematicData rather than the canonical ParsedSchematicData — none of the populated fields would have reached the analyzers even with AC1-AC3 done. The new altium_to_parsed_schematic() converter, wired into SchematicParserFactory.parse(), closes that gap.