Stage2 compile only (#12)

* core: compile macro expanders via staged bootstrap (Stage 2 Task 1)

Macros are now compiled, not interpreted, by steady state — matching
Clojure (macros are ordinary compiled fns the Java seed compiles for
clojure.core) and ClojureScript (macros compiled, invoked at compile
time). Neither reference keeps an interpreted-closure fallback.

The early macros (00-syntax) are defined while the self-hosted analyzer
is still being bootstrapped (it builds lazily after the overlay loads),
so macro-compile-hook returns nil and they get an interpreted closure.
The bootstrap compiler.janet can't substitute (it punts on syntax-quote,
which nearly every expander uses).

Fix = staged bootstrap, the same pattern as the compiler fixpoint:
defmacro stashes the expander source on the var (:macro-src) plus a
:macro-uses-env flag; once the overlay + analyzer are fully built,
backend/recompile-macros! (via ensure-macros-compiled! at the end of
load-core-overlay!) compiles each stashed expander through the now-live
analyzer and rebinds the var, marking :macro-compiled. Idempotent;
&env/&form macros keep the interpreted closure (the compiled fn* has no
such params). The interpreter is now a build-time crutch, gone by
steady state.

Rewrote if-not/if-let/if-some/assert from '& [else]' rest-destructuring
(which the analyzer punts on) to a plain rest param + (first rest), so
all 47 overlay macros compile. Analyzer rest-destructuring gap: jolt-f79.

47/47 overlay macros compiled, 0 interpreted; user macros compile
immediately post-init. Gate green: conformance 267x3, fallback-zero
31/5, bootstrap-fixpoint stage1==2==3, self-host, staged-bootstrap,
lazy-infinite 44/44, clojure-test-suite >=4034/67, sci-bootstrap,
features 78/78, all unit+spec, core-bench neutral.

* core: wrap macro expanders in fn (not fn*) so destructured arglists compile

Follow-up to the staged macro-compile change. The macro-recompile pass
wrapped each expander in the raw fn* primitive, which punts on a
destructuring rest param — so if-not/if-let/if-some/assert (using the
canonical '& [else]') couldn't compile and had been rewritten to plain
rest params as a workaround.

Root cause: fn* is the primitive; the fn MACRO is what desugars
destructuring (rest, map, nested) into the body before lowering. Wrapping
expanders in fn instead of fn* compiles any destructured macro arglist
uniformly, so the workaround is unnecessary — reverted those 4 macros to
the canonical '& [else]' forms.

Net: rest-destructuring is fully compiled for all normal code (fn/defn/
let/macro params). Only the hand-written raw fn* primitive still punts
(jolt-f79, downgraded to P4 — falls back to interpreter, still correct).

47/47 overlay macros compiled. Gate green: conformance 267x3,
fallback-zero 31/5, bootstrap-fixpoint stage1==2==3, self-host,
staged-bootstrap, lazy-infinite 44/44, clojure-test-suite >=4034/67,
sci-bootstrap, features, all unit+spec.

* core: fn*/let*/loop* are plain-symbol primitives, matching Clojure (jolt-f79)

jolt-f79 asked to compile destructuring in fn* rest params. Checking
against Clojure inverts the premise: Clojure's fn* REJECTS destructuring
at compile time ('fn params must be Symbols'; let*/loop* 'Bad binding
form, expected symbol'). So the self-hosted analyzer was already correct
— fn*/let*/loop* are plain-symbol primitives; the fn/let/loop/defn
MACROS desugar destructuring. The real defect was the interpreter
leniently destructuring raw fn*, and defn emitting raw fn* to rely on it.

Changes:
- evaluator: fn*/let*/loop* now reject non-symbol binding forms with
  Clojure's exact messages (require-symbol-params/plain-sym?), so the
  interpreter agrees with the analyzer + Clojure.
- 00-syntax: defn emits the fn MACRO (not raw fn*) so destructuring
  params desugar; unnamed, so self-recursion still resolves via the var.
- 00-syntax: completing that exposed a real gap — the overlay destructure
  fn didn't handle kwargs (a map pattern bound against a fn's sequential
  rest); it had only worked via the interpreter's destructure-bind. Added
  the seq->map coercion to the map? branch (sequential: 1 map elt => that
  map, else apply hash-map), matching destructure-bind so interpret ==
  compile.

Net: fn*/let*/loop* are plain-symbol primitives across interpreter,
analyzer, and Clojure; all real destructuring (fn/defn/let/loop/macro
params, incl kwargs & {:keys}) compiles through the macros with no
interpreter fallback. Regression spec added.

Gate green: conformance 267x3, fallback-zero 31/5, bootstrap-fixpoint
stage1==2==3, self-host, staged-bootstrap, lazy-infinite 44/44,
clojure-test-suite >=4034/67, sci-bootstrap, features 78/78, all
unit+spec (destructuring 50/50).

* docs: clarify fn*/let*/loop* take plain symbols only (jolt-f79)

grammar.ebnf: the destructuring note already attributed patterns to the
binding MACROS; make the boundary explicit — the fn*/let*/loop* PRIMITIVES
they desugar to take plain symbols only (a non-symbol binding errors, as
in Clojure).

self-hosting-compiler.md: the 'compile destructuring via a shared
destructure expander instead of falling back' item is done (and its
jolt-7dl ref was stale) — destructuring now compiles through the
fn/let/loop/defn macros' desugaring; the primitives reject patterns.

* core: Stage 2 Task 2 tier 1 — compile syntax-quote + definterface/extend/proxy

First slice of moving stateful forms onto the compile path (jolt-eaa).
- loader stateful-head?: drop syntax-quote (the analyzer's `handled` set
  already compiles it; routing it to the interpreter was redundant).
- host_iface special-names: drop definterface/extend/proxy (stub macros
  expanding to def/nil — their expansions compile once unpunted).
- letfn stays interpreted: its let* expansion needs letrec semantics
  (mutual recursion between the fns), which sequential compiled let* lacks
  — a later tier.

Gate green: conformance 267x3, fallback-zero 31/5, bootstrap-fixpoint
stage1==2==3, self-host, staged-bootstrap, clojure-test-suite >=4034/67,
features 78/78, all unit + protocol/multimethod/macro specs.

---------

Co-authored-by: Yogthos <yogthos@gmail.com>

doc/grammar.ebnf

@@ -164,8 +164,11 @@ feature         = ":clj" | ":cljs" | ":default" | keyword ;
 tagged-literal  = "#" , symbol , ws , form ;
 
 (* ── Destructuring (semantics, not reader syntax) ────────────────────────────
-   The reader produces plain vectors and maps; the binding forms (let, fn, loop,
-   doseq, for, defmacro params, …) interpret them as destructuring patterns:
+   The reader produces plain vectors and maps; the binding MACROS (let, fn, loop,
+   doseq, for, defmacro params, …) interpret them as destructuring patterns. The
+   PRIMITIVES they desugar to — fn*, let*, loop* — take plain symbols ONLY (a
+   non-symbol binding is an error, as in Clojure: "fn params must be Symbols" /
+   "Bad binding form, expected symbol"). The grammar of a pattern:
 
      binding        = symbol | seq-binding | map-binding ;
      seq-binding    = "[" , { binding } , [ "&" , binding ] , [ ":as" , symbol ] , "]" ;