feat(lang): backtick raw identifier in every binding form + raw-not-a-type + foreign reserved-name fn bare-call [F0.6]

Completes the issue-0089 backtick raw-identifier / `#import c` exemption
across all remaining identifier positions and closes three boundary gaps
the F0.6 review found.

1. Exhaustive raw-binding coverage. The `is_raw` bit now threads through
   `ast.Identifier` and EVERY binding/capture form — `IfExpr`/`WhileExpr`
   optional bindings, `ForExpr` capture + index, `MatchArm` capture,
   `CatchExpr`/`OnFailStmt` tag bindings, `DestructureDecl` per-name, and
   the protocol-default-body / foreign-class method param lists — not just
   `var_decl`/`param`. `UnknownTypeChecker` skips the reserved-name check at
   each arm when raw, so a backtick works in every identifier position while
   a bare reserved spelling still errors (issue 0076 preserved).

2. Raw identifier is never a type. `parseTypeExpr`'s atom rejects a raw
   identifier in type position (`x : `s2 = 1`, `List(`s2)`) with an accurate
   diagnostic instead of silently type-classifying it.

3. Reserved-name function bare-callable. A bare `s2(4)` parses its callee as
   a `.type_expr` (reserved spelling); `lowerCall` now rewrites a type_expr
   callee to an identifier when a function of that name is in scope, so a
   backtick-declared sx fn and a `#import c` foreign fn whose C name collides
   with a reserved type spelling both resolve by their bare name.
   (`TypeName(val)` is not a cast, so there is no ambiguity.)

Tests: examples/0152 (every control-flow/capture form + bare ref/call/member
access), examples/1054 (catch/onfail tag bindings), examples/1139 (raw in
type position rejected), examples/1220 extended (foreign reserved-name
function bare-call). 0076 negatives 1119/1121/1122/1123/1124/1125 stay green.
Gate: zig build + zig build test + 422 examples pass. specs.md + readme.md
updated; issues/0089 RESOLVED banner refreshed.

examples/expected/0152-types-backtick-control-flow.exit

@@ -0,0 +1 @@
+0

examples/expected/0152-types-backtick-control-flow.stderr

@@ -0,0 +1 @@
+

examples/expected/0152-types-backtick-control-flow.stdout

@@ -0,0 +1,8 @@
+dstr  = 1 2
+if    = 42
+for   = 10 @ 0
+for   = 20 @ 1
+for   = 30 @ 2
+match = 10
+call  = 11 11
+field = 7 9 | 7 9

examples/expected/1054-errors-backtick-reserved-binding.exit

@@ -0,0 +1 @@
+0

examples/expected/1054-errors-backtick-reserved-binding.stderr

@@ -0,0 +1 @@
+

examples/expected/1054-errors-backtick-reserved-binding.stdout

@@ -0,0 +1,5 @@
+classify(-1) = 1
+classify(0)  = 2
+classify(5)  = 10
+cleanup: bad
+done

examples/expected/1139-diagnostics-backtick-raw-not-a-type.exit

@@ -0,0 +1 @@
+1

examples/expected/1139-diagnostics-backtick-raw-not-a-type.stderr

@@ -0,0 +1,5 @@
+error: `s2` is a raw identifier, not a type — the backtick escape names a value, never a type
+  --> examples/1139-diagnostics-backtick-raw-not-a-type.sx:10:10
+   |
+10 |     x : `s2 = 1;
+   |          ^^

examples/expected/1139-diagnostics-backtick-raw-not-a-type.stdout

@@ -0,0 +1 @@
+

examples/expected/1220-ffi-c-import-reserved-name-params.stdout

@@ -1,3 +1,4 @@
 pick(10,20,0) = 10
 pick(10,20,1) = 20
 sum(10,20)    = 30
+s2(4) bare    = 104