fix(graph): lay out tasks by dependency flow

[thinksyncs]

Summary

• Replace the GraphView grid with a dependency-flow layout.
• Keep task relationships readable across dense and disconnected graphs.

Changes

• Arrange connected components by dependency level and work focus.
• Render Start/End boundaries, directional lines, fan buses, outer corridors, and crossing bridges.
• Preserve zoom and pan while keeping the complete routed graph available to Fit.
• Add regression coverage for dense graphs, cycles, boundary ports, routing, and stable refreshes.

Testing

• pnpm test: 57 passed, 1 skipped; 463 tests passed, 1 skipped
• pnpm run typecheck
• pnpm run lint
• pnpm run format
• pnpm run compile
• pnpm run audit
• Development Extension Host DOM, zoom, and pan check
• Packaged 0.6.3 VSIX install and Extension Host activation smoke test

Notes

• The current branch contains the latest origin/main.
• The all-worktree guard still reports two unrelated stale worktrees: beads-git-graph-neo-git-graph-1oj and .git/beads-worktrees/beads-sync. They were not modified.