Replace sharp with jpeg-js + exif-reader; add bun compile binary

sharp was the only native dependency preventing a single-file binary.
Replaced with:
  - jpeg-js (pure JS) for JPEG decode/resize/encode in thumbnail gen
  - exif-reader (pure JS) for EXIF tag parsing
  - Raw JPEG APP1 marker extraction for EXIF segment discovery
  - Raw XMP packet extraction from file bytes

make build-bin produces a ~59MB self-contained Mach-O binary via
bun build --compile (bun installed via nix-shell). Zero runtime
dependencies. Tested: login, whoami, collections, files all work
from the compiled binary.

bin/quak.ts: init() called once at program start before commander
parses, so libsodium is ready for all commands including those that
restore sessions from disk.

118 tests pass.

bin/quak.ts

@@ -477,4 +477,5 @@ helper
         process.exit(results.some((r) => !r.success) ? 1 : 0);
     });
 
+await init();
 program.parse();