feat(runtime): swallow() helper replaces empty catches in inlined runtime

After hf#641 inlined the runtime IIFE into every bundle, lint tools
inspecting bundled output (including Abhay's c2v eval) started flagging
empty `catch {}` blocks across the runtime. The source had explanatory
comments inside, but esbuild's minifier strips them — the IIFE ships
~10 visible patterns of `}catch{}` and consumers' linters fire on each.

Each empty catch is intentional best-effort error swallowing —
postMessage to a parent frame that may not exist, `media.play()` /
`pause()` that throw under autoplay restrictions, timeline `seek()` on
a disposed timeline, anime.js / lottie feature detection on hosts that
don't load those libraries, etc. The right behaviour stays "tried,
didn't work, move on", but doing it visibly improves three things:

  - lint clean: helper call is a real statement; no `no-empty` warnings
    survive minification
  - debuggable: flip `window.__hfDebug = true` in DevTools to see every
    swallow site with `console.debug` (silent in prod by default)
  - observable: studio / embeddings can install
    `window.__hf.onSwallowed = handler` to collect runtime swallow
    events without polluting the page console

Implementation: `packages/core/src/runtime/diagnostics.ts` exports
`swallow(label, err?)`. 41 catch sites across 12 runtime files
converted via mechanical pass (auto-generated `runtime.<module>.siteN`
labels — labels can be tightened site-by-site as a follow-up; the
shape of the change is what matters here).

Verification:
- core 674/674 (incl. 6 new diagnostics tests covering silent default,
  __hfDebug logging, legacy __HYPERFRAMES_DEBUG flag, handler hook,
  handler-throws-doesn't-recurse, both-active)
- typecheck clean
- format / lint clean
- runtime IIFE rebuilds successfully (`bun run build:hyperframes-runtime`)

Refs Abhay's c2v eval — bundler artefacts now lint-clean with the
runtime body inlined.

packages/core/src/runtime/startResolver.ts

@@ -1,4 +1,5 @@
 import type { RuntimeTimelineLike } from "./types";
+import { swallow } from "./diagnostics";
 
 const AUTHORED_DURATION_ATTR = "data-hf-authored-duration";
 const AUTHORED_END_ATTR = "data-hf-authored-end";
@@ -118,8 +119,9 @@ export function createRuntimeStartTimeResolver(params: {
             if (Number.isFinite(timelineDuration) && timelineDuration > 0) {
               resolved = timelineDuration;
             }
-          } catch {
+          } catch (err) {
             // ignore broken timeline impls
+            swallow("runtime.startResolver.site1", err);
           }
         }
       }