#56 repo.git is 260 files / 226 loose objects (Pages 20k-file cap, dumb clone = 1 GET per object)

Follow-up to #55 (same root cause, different symptom). The export path produces a bloated multi-file artifact.

Measured on this repo (318 tracked files):

today (git clone --bare):       files=260  du=2.2M  loose=226  packs=3
bundled (clone from .bundle):   files=24   du=796K  loose=0    packs=1

Two costs:

1. Dumb HTTP fetches loose objects one request each: a clone of the current export issues 200+ GETs for a toy repo. Great for nobody, pathological on a high-latency link.
2. Cloudflare Pages free tier limits a deployment to 20,000 files and 25 MiB per file. A mid-size repo (thousands of commits, loose objects) exceeds the file cap and the deploy fails outright. This is the exact target platform for the dumb-clone design.

Same fix as #55: build repo.git from the existing repo.bundle, which yields exactly one pack and no loose objects.

Verified: packed-only export + update-server-info serves and clones correctly (git clone -b master http://127.0.0.1:39401/repo.git -> tip matches).

Acceptance:

• a build's repo.git contains exactly 1 .pack and 0 loose objects (git count-objects -v shows count: 0)
• total file count under repo.git stays < 40 for the fixture repo (hooks/description noise removed)
• git clone <origin>/repo.git still works over hu13 serve
• docs state the Pages limits and that a single pack keeps us under them