feat(pcb): update placed footprints from libraries

[TWT233]

Summary

Add update_footprints_from_library to the pcb_components toolset so an agent can refresh already placed footprints after their linked KiCad library definitions change.

The tool supports exact reference and library-ID filters, defaults to a non-mutating dry run, and reports changed domains before applying. It refreshes losslessly supported library-owned pads, graphics, fields, attributes, metadata, and 3D models while preserving board-owned instance state and pad nets.

Closes #231

Approach

KiCad 10's IPC API does not expose a native "Update Footprints from Library" command, so this implements the operation as a typed planner and merge:

• resolve the explicitly requested live board and selected footprint libraries;
• parse supported .kicad_mod content into IPC footprint definitions and fail closed on unsupported/lossy clauses;
• merge library-owned content with preserved KIID, placement, side, rotation, lock state, schematic metadata, instance fields/overrides, and nets by logical pad number;
• transform back-side definitions with KiCad's exchange-footprint semantics;
• canonicalize KiCad protobuf round-trip defaults, ordering, polygon cycles, and equivalent enum values before deciding whether a footprint changed;
• apply all selected updates in one UpdateItems batch inside one KiCad undo commit.

A reviewed dry run returns plan_revision; apply requires that exact revision. Any selected conflict or stale revision prevents the batch from being sent.

Compatibility and safety

• Adds one public MCP tool; existing tools and arguments are unchanged.
• Operation is live-KiCad-IPC-only and validates the requested active board. There is no closed-board text-editing fallback.
• dry_run defaults to true; dry_run=false requires expected_plan_revision from a current plan.
• Missing libraries, duplicate/missing selected references, unsupported footprint content, removed connected pads, and stale board/library inputs return conflicts without mutation.
• Apply uses one batch and one undo transaction; an IPC update failure drops the commit rather than leaving a partial refresh.
• Layer handling now composes with [BUG] Dwgs.User footprint graphics can crash KiCad during live placement #237: footprint refresh routes through build_footprint_item, so root, pad, and graphic layers use try_layer_from_name and an unrepresentable layer is refused before anything reaches KiCad.
• Tool counts and bundled library/PCB workflow guidance are updated to 204 registered tools / 210 including meta-tools.
• Rollback is a normal KiCad undo for an applied operation, or reverting this PR for the public tool addition.

Current branch status

Rebased-equivalent merge commit 5f330fe brings the branch onto post-v0.6.1 main, including #229, #230, and #237. The PR is CLEAN / MERGEABLE at head 5f330fe90e6ec513c76dc38044b679bdb8b6ee38.

Validation

Local validation on this branch:

• cargo fmt --all -- --check
• cargo clippy --workspace --locked --all-targets -- -D warnings
• cargo test -p konnect-core --locked pcb_footprint_update::tests (21 passed)
• cargo test --workspace --locked --lib --tests -- --skip update_symbols_from_library_refreshes_a_stale_embedded_copy --skip update_symbols_from_library_refuses_a_moved_pin_unless_allowed --skip update_symbols_from_library_refuses_a_removed_pin
• cargo test --workspace --locked --doc
• git diff --check

The three skipped update_symbols_from_library_* tests fail identically on clean upstream/main@3827cdd on this host, so they are not introduced by this PR.

GitHub CI for head 5f330fe is green:

• Check & Test: ubuntu, macOS, Windows
• Clippy
• Format
• Nix flake
• Schematic viewer
• Plugin (Python)
• PCM packaging validation

Live/board acceptance from the original feature work:

• Disposable KiCad 10 live test: cargo test -p konnect --test live_kicad_tools footprint_library_update_apply_then_dry_run_is_noop --locked -- --ignored --nocapture (1 passed). It created and placed a fixture, changed its library pads/graphics/metadata/model, completed dry-run -> apply -> noop, then ran DRC.

Review checklist

• The diff is focused and contains no generated output, personal data, or unrelated cleanup.
• New names follow docs/NAMING_CONVENTIONS.md; no existing public name changes require migration handling.
• New behavior and failure paths have regression coverage.
• File/library reads fail closed; live PCB mutation preserves unrelated content.
• IPC mutations verify the requested board and do not leave partial batches.
• Registry, tool-directory.md, DEV.md, README, plugin, and packaging counts are synchronized.

[mixelpixx]

Status at Round 12: your main-merge resolved the layer_from_name reconciliation cleanly — thank you for taking that on before I got to it. The branch is conflict-free against main as of v0.7.0. What remains on my side before merge: the three review nits (the module-wide #[allow(dead_code)], the tcp://never-dialed client built to reach a pure builder, and preserved defaulting rather than deriving) plus a live run of update_footprints_from_library against a KiCAD session — this tool rewrites placed footprints, so it gets the same live gate flip_component got. That's scheduled next round; nothing needed from you.