Fix potential crashes and unhandled exceptions in character helper functions (Batch char-9)

[Ra229287]

This PR fixes bugs #1240 to #1244.

Packet

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    "type": "bug",
    "severity": "medium",
    "title": "Potential unhandled crashes in character helper functions (Batch char-9)",
    "actual_behavior": "Various character functions crashed with raw tracebacks when variables did not conform to expected formats.",
    "expected_behavior": "All helper functions should gracefully check parameter structures and parameter types, falling back to safe defaults without tracebacks.",
    "repro_steps": [
      "Pass invalid types to load_surface_overlay in src/spark_character/persona.py",
      "Pass invalid types to detect_provider_kind in src/spark_character/persona.py",
      "Pass invalid types to validate_persona_version in src/spark_character/persona.py",
      "Pass invalid types to protect_latest_pointer in src/spark_character/persona.py",
      "Pass invalid types to set_latest_persona_version in src/spark_character/persona.py"
    ],
    "affected_workflow": "Character pipeline life-cycle"
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  "evidence": {
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    "before_after_proof": "Before: raw traceback crashes. After: safe type validation guards prevent all tracebacks.",
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  "proposed_fix": {
    "approach": "Added explicit type checks, try-except containment guards, and fallback initializers across 5 character helper functions.",
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