feat(library): route straight edges and tidy syntax trees

[FelixTJDietrich]

Summary

This PR adds automatic routing for straight-edge diagram families and a tidy
layout for syntax trees:

• Clear connections stay straight. A connection reroutes only when it actually
  meets a node; connector crossings keep the existing line-jump presentation.
• Necessary detours keep breathing room around nodes, favor short and gentle
  paths, and never replace a readable crossing with a disproportionate trip
  around the diagram.
• Connections choose facing sides and spread sibling endpoints across shared
  borders instead of stacking on one point.
• Hand-placed routes remain exactly as drawn. Automatic bends are derived and
  never written into the diagram model.
• Syntax trees gain a Tidy tree layout toolbar action and the additive
  ApollonEditor.layoutSyntaxTree() API.

The branch is rebased directly onto the current main, which includes the
straight-edge editing work from #834.

Follow-up to the node-overlap report in #282, which was closed by the manual
straight-edge editing work in #834. Long-text wrapping is outside this PR and is
not claimed as fixed.

Why this is intentionally conservative

Automatic routing should help without making a diagram feel restless:

• The direct line has a 1 px collision guard, while a generated detour receives
  the full 10 px minimum clearance. A nearby node therefore does not trigger a
  route change just because it enters the preferred clearance halo.
• Other connections do not become routing obstacles. Crossings therefore remain
  direct and predictable, while the existing line jumps preserve readability.
• A 5% deterministic endpoint-side deadband prevents small movements near a
  node corner from flipping the connection to another side.
• While a node is moving, its valid straight-edge topology is kept for the full
  gesture. It changes immediately only if keeping it would cross a node, then
  settles to the exact route on release.
• Node drags involving straight connections use the routing worker even in small
  diagrams. The display-only handoff preserves diagonal polylines instead of
  briefly turning them into step edges.

Compatibility and failure behavior

• Existing hand-authored straight routes bypass automatic obstacle routing.
• Existing orthogonal routing is unchanged.
• Native-handle previews and commits use the same validated handle point, even
  when the pointer is off-center or nodes overlap.
• Tidy layout is one undoable operation. Valid trees and forests are arranged;
  cyclic, multi-parent, and otherwise malformed components stay where the user
  placed them.
• The toolbar waits for controlled node positions to reach React Flow and then
  performs the same inset-aware fit as the public API.
• layoutSyntaxTree() is additive and is a no-op for other diagram types.

Release note

Keep straight connections clear, stable, and responsive automatically. They now
choose facing sides, spread sibling links across shared borders, and route around
nodes without reorganizing when other connections cross them; clear shots remain
straight and hand-placed routes stay exactly as drawn. Syntax trees also gain a
one-click tidy layout that arranges valid parent-child forests while leaving
malformed portions untouched.

Implementation notes

• Routing uses a deterministic, integer-based visibility graph and A* search,
  including deterministic tie-breaking.
• The visibility graph starts with obstacles that block the direct route, adds
  newly relevant node bodies locally, and has a bounded full-field fallback.
• Third-party node bodies are never exempted when an endpoint starts inside
  their clearance halo.
• Coordinated endpoint seats keep straight-edge fans evenly distributed.
• In a new crossing-heavy 12-edge Chromium regression fixture, local profiling
  reduced the worst solve from 2,629.7 ms to 20.5 ms. This is a regression
  fixture result, not a general-purpose benchmark.
• Bundle cost remains explicit and within the existing budgets:
  • main entry: 125.72 kB / 126 kB
  • routing worker: 41.45 kB / 44 kB
  • model chunk: 5.08 kB / 8 kB
  • export chunk: 413.41 kB / 700 kB

Steps for testing

1. Open a crowded use-case, syntax-tree, or Petri-net diagram and confirm that
   straight connections avoid intervening nodes.
2. Move a node close to a clear connection without touching it; the edge should
   remain straight. Move it into the line; the edge should take a compact,
   well-cleared detour.
3. Move a node repeatedly near an endpoint-side boundary and confirm the edge
   does not jump sides on small movements.
4. Create sibling connections and confirm their endpoints fan out. Cross two
   connections and confirm they remain direct and use the existing line jump.
5. Add or move a manual bend, then place a node over that route. The authored
   route should remain exactly as drawn.
6. Drop a connection off-center within a native handle and confirm the committed
   endpoint exactly matches the preview.
7. Apply Tidy tree layout to a valid forest and confirm one-step undo and an
   inset-aware fit. Repeat with cyclic or multi-parent content and confirm the
   malformed components are not rearranged.
8. Call ApollonEditor.layoutSyntaxTree() on a syntax tree and on another
   diagram type; confirm layout in the former and a no-op in the latter.

Verification

• pnpm lint && pnpm format:check && pnpm build && pnpm test
  • 95 test files passed
  • 1,860 tests passed; 1 skipped
• Fresh production-build Chromium interaction run:
  • 17/17 targeted connection and straight-edge UX tests passed
• Fresh production-build crossing-heavy performance regression:
  • passed 5/5 Chromium runs and 5/5 Firefox runs at the 34 ms p95 frame budget
• pnpm --filter @tumaet/apollon size
  • all four published bundle budgets passed

Screenshots / screencasts

Captured from this branch's production build after choosing Tidy tree layout.
Deterministic geometry fixtures cover route quality and failure cases beyond this
representative diagram.

Checklist

• Linked the applicable portion of Syntax tree diagram: long text overlaps nodes (needs line wrapping) #282
• Added a user-facing changeset
• Used a Conventional Commit PR title matching the user-visible feature
• Added unit and browser interaction coverage
• Passed the complete local pre-PR gate
• Kept published bundles within their documented budgets
• Documented the additive public API inline
• Included a representative screenshot

[Claudia-Anthropica]

@FelixTJDietrich The deterministic routing and tidy-tree work is thoughtfully structured, but the new straight router can still pass through a nearby node and can miss sibling-only crossings. Native-handle commits can also diverge from the preview; I left the concrete fixes inline.

[Claudia-Anthropica]

@FelixTJDietrich The follow-up fixes address the obstacle-halo, sibling-crossing, and native-handle preview/commit issues from my previous review, with focused regressions covering each path. The relevant local unit suites pass, so this looks good to merge.

[Claudia-Anthropica]

@FelixTJDietrich The new commits preserve obstacle-body safety while stabilizing straight-edge routing, aimed-outline previews, and worker-backed interaction performance. The previous findings remain resolved, all captured CI checks pass, and I found no current blocking defect.