De-fork spike S3: HardPolicy kill gate (non-bypassable DDL denies at every dispatcher)

Stage S3 of the de-fork spike — the kill gate. Enforce non-bypassable hard denies (sql_execute DDL: DROP DATABASE/SCHEMA/TRUNCATE; bash DDL) at EVERY model-invoked tool-execution dispatcher, preserving today's behavior (these already block; S3 relocates them to one audited chokepoint).

- NEW \`packages/opencode/src/altimate/policy/hard-policy.ts\` — pure/synchronous/total \`HardPolicy.check()\`; malformed args fail closed (policy_internal_error), never throws/implicit-allows. Emits a structured audit record per call (the oracle — NOT the trace).
- HardPolicy.check inserted before tool.execute at all active + latent dispatchers (D1/D2/D6 in session/prompt.ts, D3/D4 in session/tools.ts, D5 in tool/batch.ts) + fail-closed init in effect/app-runtime.ts.
- Fixes a real bypass: the fork's resolvers discarded \`tool.execute.before\`'s return value, so a before-hook that mutated args (SELECT -> DROP DATABASE) executed the mutation unchecked. S3 captures the post-hook FINAL args and checks THOSE.
- 18 tests (bypass matrix): allow-all config still denies; near-miss controls run; deny is terminal (execute + tool.execute.after skipped); audit oracle asserted.

This is a security boundary + the spike's decision checkpoint. HELD for human go/no-go — do not auto-merge.