feat: execute Phase 1 architectural hypermedia framework
- Bootstraps `src/core/` foundation (`db.ts`, `valkey.ts`, `spire_ffi.ts`, `main.ts`).
- Adds `auth_guards.ts` for payload capping, CSRF check, and rate limiting.
- Adds `content_negotiation.ts` and `sse_adapter.ts` for Datastar transport helpers.
- Adds `error_fragments.tsx` for standardized Datastar error morphs.
- Introduces `scripts/lint_arch.ts` to block imperative DOM usage.
- Updates `deno.json` with src workspace configs and lint commands.
Co-authored-by: mrteye <1945243+mrteye@users.noreply.github.com>
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