Add first-pass runtime-causality contracts v0

[mdheller]

This PR adds the first slice of runtime-causality contracts, including four schemas and four example files derived from ordered diagnostic logs. It collapses repeated failures, security verdicts, network truth ambiguity, and browser preflight transactions into typed, bounded records.

• Schemas: RetryLoopFingerprint, SecurityVerdictState, NetworkTruthState, BrowserLaunchTransaction
• Examples for each schema
• Documentation in docs/contract-additions/runtime-causality-contracts-v0.md

This prepares the SourceOS spec for reproducible diagnostics, browser/terminal child-process validation, and mesh/network intelligence evidence recording.

[mdheller]

Expanded runtime-causality scope

This PR has been extended beyond the original four-schema first-pass slice. Current branch scope now includes ten runtime-causality contract families:

1. RetryLoopFingerprint
2. SecurityVerdictState
3. NetworkTruthState
4. BrowserLaunchTransaction
5. RuntimeIdentityGraph
6. DesktopServiceBrokerState
7. MaintenanceEpoch
8. RuntimeRegistryIntegrityRecord
9. BootSessionPhaseState
10. DiagnosticStormRecord

Each schema has a corresponding example payload.

The documentation in docs/contract-additions/runtime-causality-contracts-v0.md has been expanded to describe the complete ten-contract surface, downstream consumers, and the intended runtime flow:

1. capture raw telemetry;
2. normalize repeated signatures into retry/storm records;
3. attach network, security, boot/session, and registry context;
4. gate browser/terminal launches through identity and broker preflight;
5. bound maintenance work with explicit epochs and emission budgets.

Remaining follow-up after this PR:

• add central schemas/README.md catalog rows;
• add validation automation for schema/example mapping;
• add a reusable ordered-log parser that emits these records;
• wire SourceOS shell, BearBrowser, TurtleTerm, MeshRush, and Prophet Platform consumers.