Codex harness capture

[dbtlr]

Summary

Adds the first Codex capture slice for Saga:

• installs, reports, and uninstalls project-local Codex hooks via saga harness install/status/uninstall codex
• writes a runnable project-local hook shim that calls saga ingest codex-hook
• records Codex hook payloads as append-only raw events with workspace-scoped idempotency
• adds saga ingest codex-hook [file|-] and saga ingest recent debug surfaces
• adds the raw_events table, raw event DB helpers, collector normalization, and raw event contracts
• hardens install behavior around source binding, migration readiness, malformed hook config, and activation rollback

Validation

• pnpm --filter @saga/cli test && pnpm --filter @saga/cli check
• pnpm --filter @saga/collectors test && pnpm --filter @saga/collectors check
• pnpm --filter @saga/db test && pnpm --filter @saga/db check
• pnpm exec vp check --fix
• pnpm run verify
• pnpm run build
• local Postgres hook E2E smoke executed the exact installed Codex hook command and verified a persisted codex.Stop raw event
• adversarial phase reviews were run until no blocking/actionable issues remained