Add graph exploration workspace and replayable investigations

[aaltshuler]

Graph exploration previously required composing separate search, inspection, and table surfaces while keeping expansion intent outside saved views. This adds an optional GraphExplorer workspace and source-bound investigation checkpoints that replay paginated requests with fresh cursors.

• Add passive bounded neighborhoods, typed/directional/paginated expansion, cancellation/progress, and explicit layout preservation.
• Add ordered connection explanations with visible/loaded graph choices and distinct missing, filtered, unreachable, and hop-limit outcomes.
• Add node/relationship/selection inspection, explicit search recovery, persistent search/table intent, named checkpoints, notes, and import/export. Reconcile expansion recipes with undo/redo and guard unrelated expansion ownership during restore.
• Integrate the workspace across demo data modes with browser checkpoint storage and responsive layout.
• Add seven runnable Storybook workflows, a fictional asynchronous supplier service, source examples, and an exploration guide.

Validation:

• pnpm check: 1,888 tests plus 23 performance-gate tests, lint, types, boundaries, anchors, and engine pin check.
• Package builds and pack smoke, including publint, attw, tree-shaking, and worker asset checks.
• Demo and Storybook production builds; Node import probes and engine-free SVG fixture.
• All seven Storybook workflows driven in a browser, including remote search recovery, pagination, comparison, ordered paths, cancellation, and checkpoint reopen across fresh canvas and reload.
• All 50 demo scenarios validated: the full regression run plus a successful focused recheck of context recovery and the new CSV journey after correcting toolbar placement. The new journey covers filtering, path retention, restore, responsive bounds, and source-mismatch rejection.

Checkpoint replay requires the referenced source and services. Restore is a sequence of operations: failure retracts restore-owned contributions but does not reconstruct the previous investigation or reverse host loader/filter effects. Storage and source loading remain host responsibilities. This change makes no new GPU performance claim.