chore: remove all source code comments and internal artifacts

Strip every comment from the source (parsed with the TypeScript compiler so
strings, template literals, regex literals and JSX are never touched), and drop
internal/working artifacts that do not belong in the public repository
(design mockups, internal analysis docs, a stray backup file and an old log).
No functional change: build is green, the full test suite passes.

tests/download-completion.test.ts

@@ -26,8 +26,6 @@ describe("download-completion", () => {
     const contentLength = (n: number) => ({ expectedTotal: n, source: "content-length" as const, canFinishEarly: true });
     const providerMeta = (n: number) => ({ expectedTotal: n, source: "provider-metadata" as const, canFinishEarly: false });
 
-    // H3 regression: a stream-end download (no Content-Length, no provider size)
-    // that yielded 0 bytes is a FAILED download, not a valid completion.
     it("rejects a 0-byte stream-end download (H3)", () => {
       const result = validateDownloadedFileCompletion({ actualBytes: 0, plan: streamEnd });
       expect(result.ok).toBe(false);
@@ -57,7 +55,6 @@ describe("download-completion", () => {
 
     it("accepts provider-metadata download and flags size mismatch", () => {
       const result = validateDownloadedFileCompletion({ actualBytes: 1900, plan: providerMeta(2000), toleranceBytes: 0 });
-      // provider-metadata: shorter than expected -> underflow rejected
       expect(result.ok).toBe(false);
     });
   });