Guard config contracts at startup

[gphiIIips]

Summary

• Make 41 existing literal typed-store fallback values explicit in PARAMETERS.
• Add centralized startup config validation in src/config_validation.rs, called once before Simulation::new.
• Record validation status in startup logs, run metadata, and the compact [report] line.
• Extend Fast Guardrails with runtime validation tests.

Why

Silent fallback values and malformed config values are scientifically risky: a missing or invalid parameter can change model behavior without the operator realizing it. This PR makes the currently used literal defaults auditable and adds a startup boundary that stops unambiguous invalid config before timestep 0.

Runtime Behavior

• Default mode is strict.
• On success, startup logs show [config-validation] PASSED: 0 error(s), 0 warning(s), mode=strict.
• Hard errors block the run before Simulation::new, write failed run metadata where possible, print a [report] status=config_validation_failed ..., and exit with code 2.
• AMR_CONFIG_VALIDATION=warn allows explicit non-production continuation while preserving the failed validation status in logs/metadata/report output.

Hard errors currently cover:

• literal get_global_param keys missing from PARAMETERS;
• required get_required keys missing from PARAMETERS;
• literal get_or_default(map, "...") keys missing from PARAMETERS;
• non-finite values;
• out-of-range probability-style values;
• negative values for clearly non-negative parameter families.

Warnings currently cover:

• boolean-style flags set to values other than 0.0 or 1.0, because runtime treats >0.5 as true.

Scope

• Production model transition logic is not touched.
• Existing model behavior should be unchanged when config is valid.
• Dynamic per-entity fallback patterns remain intentionally allowed.

Validation

• cargo check --all-targets
• cargo test --test config_validation -- --nocapture
• cargo test --test config_invariants -- --nocapture
• cargo test --test probability_invariants -- --nocapture
• cargo test --test determinism -- --nocapture
• cargo test --test csv_invariants -- --nocapture
• cargo test --test dimension_invariants -- --nocapture
• rustfmt --check src/main.rs src/observability.rs src/config_validation.rs tests/config_invariants.rs tests/config_validation.rs tests/csv_invariants.rs tests/determinism.rs tests/dimension_invariants.rs tests/probability_invariants.rs
• git diff --check

Runner Smoke

• JID: 20260612T001542-58395
• Overrides: population_size=1000, time_steps=200, CalibrationMode::Partial, seed 123456789
• Result: success
• Startup validation line: [config-validation] PASSED: 0 error(s), 0 warning(s), mode=strict
• Simulation run ID: 870119
• Summary hash: f5a194b21e63bfcc58d95ba91c7b35649c3158667752dc48f9a40bebb7263299