Define Zeliard 2 content schemas and stable IDs

[nolanvenhola]

What changed

• defines typed Godot Resources for campaigns, regions, rooms, actors, enemies, items, abilities, dialogue, quests, assets, and events
• adds typed nested records for room exits, placements, dialogue lines, quest stages, and event steps
• establishes path-independent kind:name content IDs and typed reference expectations
• adds a runtime content catalog plus graph validation for malformed, duplicate, missing, and wrong-kind IDs
• updates Zeliard Creator to validate the same complete content graph
• documents definition ownership and the strict separation between immutable authored definitions and mutable runtime/save state
• adds a reviewable 12-resource example campaign with two linked rooms and newly authored programmer art

Acceptance evidence

• representative content round-trips through text Resource save/load without semantic loss
• campaign identity survives an actual file move and rename
• missing targets, wrong target kinds, duplicate IDs, and kind/namespace mismatches are detected
• all 11 required top-level schema kinds are loaded from the example catalog
• source files remain human-reviewable .tres resources

Validation

• architecture and typing rules: PASS (25 scripts)
• production content scenarios: PASS (9 tests)
• Creator EditorPlugin startup: PASS
• main scene smoke: PASS
• Windows release export and executable smoke: PASS
• Web release export: PASS

No original Zeliard assets or legacy resource formats are used. Save versioning, migration, recovery, and structured diagnostics remain scoped to #241.

Closes #240