feat(navigation): resolve exact cross-probe targets

[neusse]

Closes #395.

This is the terminal N6 slice of the approved Navigation MVP. It reconstructs the unique cross-probe work from draft #401 directly on current main after #488, #491, #492, #493, and #494 landed. The rejected #400 activation tool is intentionally absent. Original implementation authorship from @dubesinhower is preserved.

User-visible capability

• Adds the read-only resolve_cross_probe_target tool with the exact maintainer-approved public name.
• Resolves schematic symbol to PCB footprint and PCB footprint to schematic symbol from saved KiCad symbol-path linkage.
• Requires explicit project identity, both saved documents, the exact schematic instance path, source editor, and source KIID.
• Returns exact source and destination identities plus separate saved-structure and live-document evidence.
• Proves both requested documents through typed GetOpenDocuments IPC readback.
• Refuses missing, duplicate, malformed, stale, instance-inconsistent, and reference-inconsistent linkage with structured errors.
• Performs no activation, reveal, viewport, selection, raw-action, mouse, or keyboard side effects.

Navigation MVP acceptance accounting

1. Editor, version, document, sheet-instance, active-state availability, and capability observation: feat(navigation): observe editor capabilities #488 and test(navigation): complete unavailable capability matrix #494.
2. Deterministic C10 to exact schematic KIID/instance resolution: feat(navigation): resolve exact editor targets #492.
3. Exact activation or typed unsupported: feat(navigation): observe editor capabilities #488/test(navigation): complete unavailable capability matrix #494 report activation, reveal, center, and fit unavailable; per the maintainer decision no public pretend-to-act tool ships.
4. Exact selection and full readback: feat(navigation): observe exact editor selection #491 observes selection and feat(navigation): verify editor selection mutations #493 verifies clear/add/remove mutations by complete readback.
5. Exact cross-probe to one PCB footprint KIID: this PR.
6. PCB destination action or typed unsupported: this PR returns the destination without side effects; feat(navigation): verify editor selection mutations #493 provides the supported exact selection operation, while feat(navigation): observe editor capabilities #488/test(navigation): complete unavailable capability matrix #494 report activation unsupported.
7. Destination document and selection proof: this PR proves the destination document; feat(navigation): observe exact editor selection #491/feat(navigation): verify editor selection mutations #493 provide exact selection observation/mutation readback when the client requests it.
8. Structured ambiguity, stale, wrong-context, closed-editor, unresolved-destination, unsupported, and readback-mismatch refusals: covered across feat(navigation): observe editor capabilities #488, feat(navigation): observe exact editor selection #491, feat(navigation): resolve exact editor targets #492, feat(navigation): verify editor selection mutations #493, and this PR.

This closes the issue under the smaller five-operation composition explicitly approved in the maintainer decision.

Current-main conflict resolution

The old #401 branch also contained #400's rejected activation API and stale generated counts. The reconstruction keeps current-main board safety and capability-model changes, excludes activation completely, and adds only the cross-probe resolver. Tool counts were regenerated rather than hand-merged.

Evidence

• cargo test -p konnect-core cross_probe --lib - 7 passed.
• cargo test -p konnect-core editor_navigation --lib - 14 passed.
• cargo test -p konnect-ipc --test mock_server_test - 55 passed, 1 intentionally ignored.
• Guard-neutering proof: disabling reference agreement made missing_duplicate_and_reference_mismatch_destinations_fail_closed fail; restoring it made the test pass.
• cargo xtask fix-doc-counts --check - 21 toolsets, 226 registered, 233 total; current.
• cargo fmt --all -- --check - passed.
• cargo clippy --workspace --locked --all-targets -- -D warnings - passed.
• cargo test --workspace --locked --lib --tests - passed.
• cargo test --workspace --locked --doc - passed.
• git diff --check - passed.

Hermetic coverage includes exact forward/reverse mapping, root and nested sheet paths, human C10 resolution, missing/duplicate/mismatched linkage, stale sources, wrong instances, both live-document proofs, and absence of mutation commands.

Validation debt and boundaries

No disposable live KiCad GUI endpoint was available for a new manual integration run. The operation is focused and read-only, and its IPC and saved-design behavior is covered deterministically. Saved footprint symbol-path representation remains a KiCad-version compatibility surface. Pin/pad/net expansion remains unsupported until one stable destination can be modeled.