feat(interval): emit version-zero initial evidence

[kim-em]

Summary

• add a generic Proof.initialTarget theorem for an exact target already present in Proof.initialBase
• add a guarded RuntimeEmit fast path for empty-chronology, single-terminal, version-zero targets whose node and opaque fact are kernel-correlated with an exact caller-quoted Input
• re-run proof-registry construction under the emitter caller’s limits and retain schema, chronology, type, expression, transactional rollback, and exact Meta checking
• add a real opaque interval-fact canary through controller/lineage/Checked construction plus exact refusal canaries for proof, emitter, expression, chronology, version, and upstream lineage limits
• document the phase boundary: tree/result/edge/depth limits are consumed before a Checked value exists, while RuntimeEmit owns proof and emission budgets

Dependencies

Stacked on #9534, which is stacked on #9532. This PR deliberately targets upstream main; its diff will shrink to the single production commit as the dependencies merge.

Validation

• focused lake build for Proof, RuntimeEmit, and RuntimeEmitConformance
• dependency DAG and published trust-surface checks
• copyright, file-size, forbidden-term, and diff checks
• no rational syntax, experimental Result quotation, or ordered-constructor dependency