fix: normalize_port raises a clear error on missing/empty port

canonical_key/key()/burn on a portless proxy url used to raise a bare
ValueError from int('') instead of naming the problem, breaking burn()'s
documented not-in-pool contract. normalize_port now raises a legible
'missing port' ValueError; to_proxy() on a portless url still succeeds.

Signed-off-by: disqualifier <dev@disqualifier.me>

README.md

@@ -149,6 +149,9 @@ key (`host:port:user:pass`, or `host:port` auth-less; the port is normalized so
 differing only by password are distinct slots. `burn` on a proxy not in the pool raises
 `ValueError`; `restore` on a proxy not in the pool logs a warning and no-ops (matching
 `remove`'s contract, as of v0.3.0 — previously it silently did nothing with no signal).
+A **portless** url (`http://user:pass@host`, no `:port`) parses fine via `to_proxy()`,
+but keying it (`canonical_key`/`.key()`/`burn`/`add`/`remove`) raises `ValueError`
+naming the missing port — a proxy needs a port to have a canonical identity.
 
 ### Cooldown
 
@@ -209,6 +212,17 @@ await reset("https://provider/reset-url")    # rotate upstream ip
 
 ## Changelog
 
+### v0.3.2
+
+- **Portless proxy url now fails loud and legible.** `canonical_key`/`.key()`
+  (and therefore `burn`/`add`/`remove`) on a proxy url with no `:port`
+  (`http://user:pass@host`) used to raise a bare `ValueError("invalid literal
+  for int() with base 10: ''")` from `normalize_port('')` — an unrelated `int()`
+  error that broke `burn()`'s documented "raises ValueError naming the key if
+  not in pool" contract. `normalize_port` now raises `ValueError("missing port:
+  ...")` naming the problem instead. `to_proxy()` on a portless url still
+  succeeds (construction tolerates a missing port); only keying it raises.
+
 ### v0.3.1
 
 - **Docs-only de-bloat pass.** Compressed module/internal docstrings and comments,