Reader: #() params survive syntax-quote (auto-gensym names)

#(...) named its synthesized params with bare gensyms, so a #() written inside a
syntax-quote had its params qualified to the current ns by sq-symbol — and a
qualified symbol isn't a valid fn param. hiccup's compiler emits
`(let [sb# ..] (iterate! #(.append sb# %) ..)), which broke with "Unable to
resolve symbol: ns/_NNNN".

Name the params with a trailing # (auto-gensym suffix, like Clojure's p1__N#) so
syntax-quote maps them consistently and leaves them unqualified. Harmless outside
a backtick (just a regular symbol name).

docs/spec/02-reader.md

@@ -125,6 +125,11 @@ checks → UNVERIFIED (rows to add).
   nested form including vector, map and set literals — `#(assoc {} :k %)`,
   `#(hash-set % %2)` and `#(get {:t %} :t)` all see their `%`s. (A reader that
   scanned only call forms would miscompile `#(identity {:text %})` as a 0-arg fn.)
+- The synthesized parameters are auto-gensyms (their names carry the `#` suffix,
+  like Clojure's `p1__N#`), so an `#()` written inside a syntax-quote survives:
+  the params are mapped consistently and left unqualified rather than being
+  qualified to the current namespace (a qualified symbol is not a valid
+  parameter). E.g. ``  `(map #(inc %) xs) `` expands correctly inside a macro.
 - `#()` literals MUST NOT nest.
 
 ```clojure