Fix first-use nested history fallbacks

[SandroMaglione]

Summary

• require every history default to build a complete, schema-valid root configuration whose selected branch contains the declared history owner
• resolve first-use nested fallbacks through inactive compound and parallel ancestors while retaining already-active unaffected parallel regions
• preserve recorded shallow/deep restoration and history target/resolved-target trace identity
• extend compiler, runtime, generated reference-model, documentation, and platformer example coverage

The root cause was that the public fallback contract only allowed a direct-owner snapshot and the planner required that exact path. A globally targetable nested history state therefore had no way to supply inactive ancestor values on first use. The new owner-constrained builder/result types make unsafe partial defaults unrepresentable, while runtime validation produces a deterministic diagnostic for forged values.

Changeset

• Added or updated for a library or package-metadata change
• Not required because this PR does not change src/ or package.json

Added .changeset/calm-histories-resume.md as a patch correctness fix.

Validation

• pnpm check
• Relevant example checks, when examples changed
• Reviewed the automated type-performance report, when the public TypeScript API or inference changed

Additional validation:

• pnpm --dir examples/platformer check
• pnpm perf:types
• 337 runtime tests and 586 TSTyche assertions pass