refactor!: drop the HTTP facade and the dead SwiflowStore→SwiflowFetcher edge

[zzal]

Part-1 modularization-audit fixes (findings 1 and 3).

• BREAKING: deletes the HTTP static facade in SwiflowFetcher — eight one-line pass-throughs to HTTPClient() with zero consumers in examples or tests. Migration: HTTP.get(...) → HTTPClient().get(...); signatures are otherwise identical.
• Removes SwiflowStore's dead SwiflowFetcher dependency (import + Package.swift edge). Compile-verified unused: the target builds clean without it; the only textual match was a comment citing PR feat(fetcher): HTTPTransport seam — the client is now host-testable #160.

Whole-package swift test: 1897 tests, 350 suites, all passing.

🤖 Generated with Claude Code

[github-actions]

📦 Bundle size

Artifact	Baseline	This PR	Δ
App.wasm	5.06 MB	5.23 MB	+3.50%
App.wasm (gzip)	1.80 MB	1.87 MB	+3.57%
JS runtime	54.5 KB	54.5 KB	+0.00%
JS runtime (gzip)	11.3 KB	11.3 KB	+0.00%
Total (gzip)	1.81 MB	1.88 MB	+3.55%

✅ Within budget (≤5% growth allowed).

_{Baseline: Swift 6.3, WASM SDK 6.3-RELEASE, measured 2026-06-18.}