lib/gitea: fix the fetch-pack-over-HTTP hang — native parse fast path

The sx-forge native-loop blocker: clone! of the live giles/rose-ash
never returned over gitea/http-app. Root cause was NOT the transport —
pack-line-parse ran every pack line through the interpreted spec parser
(~6.6KB/s on the CEK machine; a full-repo pack = hours), and a non-hex
byte in a pkt length header parsed negative (index-of -1), walking the
scan index backwards forever.

- gitea/parse-obj: use the host reader (open-input-string + read,
  ~3700x faster, value-identical) when the host provides it; hosts
  without string ports keep sx-parse. Feature-detected at load.
- pkt-sections-loop: (< n 4) guard — malformed lengths error instead
  of hanging.
- push-cmd!: haves = every advertised remote ref held locally, so a
  NEW branch pushes only its delta, not the whole repo closure.
- tests/wire.sx: malformed-len errors, truncated-pkt clamps, parse-obj
  = sx-parse equivalence (blob/commit + cid). 83/83.
- tests/wire-http.sh + wire-http-client.sx: end-to-end over REAL
  http-listen/http-request on :8943 — ls-remote/clone/push-new-branch/
  fresh-clone-verify/delete. The coverage gap that hid all this.

Proven vs the live forge (in sx-gitea-1): full 4468-file clone in 77s
(was: hang), commit, push heads/sx-smoke-test ok, branch advertised on
sx.sx-web.org. Conformance 620/620.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/gitea/scoreboard.md

@@ -6,10 +6,10 @@ _Generated by `lib/gitea/conformance.sh`_
 |-------|-----:|-----:|------:|
 | repo | 91 | 0 | 91 |
 | access | 103 | 0 | 103 |
-| wire | 78 | 0 | 78 |
+| wire | 83 | 0 | 83 |
 | issues | 88 | 0 | 88 |
 | pr | 100 | 0 | 100 |
 | activity | 60 | 0 | 60 |
 | search | 35 | 0 | 35 |
 | fed | 60 | 0 | 60 |
-| **Total** | **615** | **0** | **615** |
+| **Total** | **620** | **0** | **620** |