Validate hallucination-control configuration at plugin initialization

[deepintai]

Context

The semantic cache plugin accepts hallucination-control settings (strictness level, temperature cap, technique list) but does not validate them at startup. Invalid values are silently coerced to defaults (see hallucControlStrictness() at line ~65), which can mask operator configuration mistakes.

What to do

1. Add a validation function (in main.go or a new validation.go):

   func validateHallucinationControlConfig(config *Config) error

   checking:
   • Strictness is one of "low", "medium", "high".
   • Temperature cap is within a sensible range (0.0-2.0).
   • Every entry in the techniques list is a known technique ID: grounding_directive, anti_fabrication, citation_required, uncertainty_ack, temperature_clamp.
2. Return a descriptive error naming the offending field and the allowed values.
3. Call the validator during the plugin's Init/Setup flow so misconfiguration fails fast instead of being silently normalized.

Acceptance criteria

• Invalid strictness (e.g. "invalid"), out-of-range temp cap (e.g. -1.0, 100.0), and unknown technique IDs each produce a clear validation error.
• Error messages state which field is invalid and the allowed values.
• Validation is wired into plugin initialization.
• Tests demonstrate each rule (valid config + one failing case per rule).
• go test ./plugins/semanticcache/... passes.

File pointers

• Config struct + getters: deepintshield_server/plugins/semanticcache/main.go (hallucControlStrictness:65, hallucControlTempCap:78, hallucControlTechniques:92)
• Technique IDs: deepintshield_server/plugins/semanticcache/hallucination_control.go (constants near lines 18-31)