fix(governance): reject invalid outcome budgets

[bokelley]

What

• reject negative, non-finite, and overflowing report_plan_outcome monetary values before ledger mutation
• validate completed-outcome package budgets even when committed_budget is supplied
• align the canonical source schema and training-agent tool schema
• document the experimental AdCP 3.2 migration with the required six-week notice

Why

A negative delivery spend could reduce the committed-budget ledger. Alternate completed-outcome budget shapes and floating-point overflow could also bypass the intended finite, non-negative ledger invariant.

Impact

Invalid outcomes now return VALIDATION_ERROR without changing the plan ledger or recording an audit outcome. This is an experimental-surface breaking validation change, represented by a minor changeset. Released dist schemas and package files are unchanged.

Verification

• expert security review: clean
• expert testing review: clean
• expert quality review: clean
• focused governance tests: 28 passed
• full server unit suite: 4,741 passed; one unrelated Addie test was flaky in the combined run and passed 6/6 in isolation
• TypeScript no-emit check
• schema validation: 658 schemas, 20 checks
• docs JSON schema blocks: 284/284
• docs navigation: 21/21
• immutable release artifacts
• Semgrep: 0 findings