add text-processing primitives to el runtime

24 new functions covering counting (str_count, str_count_chars,
str_count_bytes, str_count_lines, str_count_words, str_count_letters,
str_count_digits), finding (str_index_of_all, str_last_index_of,
str_find_chars), transforming (str_repeat, str_reverse,
str_strip_prefix/suffix/chars, str_lstrip, str_rstrip), character
classification (is_letter, is_digit, is_alphanumeric, is_whitespace,
is_punctuation, is_uppercase, is_lowercase), and splitting/joining
(str_split_lines, str_split_chars, str_split_n, str_join).

Phase 1 is byte-level + ASCII character classes. Unicode-grapheme
awareness, normalization, and regex are Phase 2 (filed separately).

Lexer-internal helpers is_digit, is_alpha, is_whitespace renamed to
lex_is_digit, lex_is_alpha, lex_is_whitespace to free the public names
for the runtime exports. The El compiler's lexer.el and the bundled
elc-combined.el both updated.

Codegen registrations: builtin_arity entries for all 24 functions,
is_int_call entries for the Int-returning ones (str_count*,
str_last_index_of, str_find_chars) so the + operator dispatches as
arithmetic when applicable.

Tests: tests/text/ corpus with 8 acceptance cases covering the surface
(count-substring, count-overlap-skip, count-lines-words-letters,
index-of-all, transform-suite, char-classes, split-lines, join). All
pass against a fold-fn-main-aware elc bootstrap (see ELC env var
override in run.sh).

Self-host fixed point: elc-combined.el's emit-main pass does not
currently fold the fn main body into C's main, a pre-existing
condition that surfaces as a 39-line gen2/gen3 diff with empty main
in gen3. The committed dist/platform/elc binary has the fold logic
so all tests pass against it. Filing the elc-combined fold-fn-main
fix separately. This commit does not introduce new self-host drift.

tests/text/run.sh

@@ -0,0 +1,87 @@
+#!/usr/bin/env bash
+# run.sh — build and execute the text/ acceptance corpus.
+#
+# Each examples/<case>.el is a self-contained El program with a fn main()
+# that prints a single deterministic result line. The runner compiles each
+# via the canonical native elc, links it against the shared C runtime, runs
+# it, and asserts the output matches the expected value.
+
+set -uo pipefail
+cd "$(dirname "$0")"
+
+EL_HOME="${EL_HOME:-$(cd ../.. && pwd)}"
+ELC="${ELC:-${EL_HOME}/dist/platform/elc}"
+RUNTIME_DIR="${EL_HOME}/el-compiler/runtime"
+
+if [ ! -x "${ELC}" ]; then
+    echo "elc not found at ${ELC}" >&2
+    exit 1
+fi
+
+PASS=0
+FAIL=0
+FAILED_NAMES=()
+
+run_runtime_case() {
+    local name="$1"
+    local src="$2"
+    local expected="$3"
+
+    local out_c
+    local out_bin
+    out_c="$(mktemp -t text_test.XXXXXX).c"
+    out_bin="$(mktemp -t text_test.XXXXXX)"
+
+    if ! "${ELC}" "${src}" > "${out_c}" 2>/tmp/text_test.elc.err; then
+        echo "FAIL  ${name} — elc emit failed:"
+        cat /tmp/text_test.elc.err | sed 's/^/      /'
+        FAIL=$((FAIL+1))
+        FAILED_NAMES+=("${name}")
+        rm -f "${out_c}" "${out_bin}"
+        return
+    fi
+
+    if ! cc -O2 -I "${RUNTIME_DIR}" "${out_c}" "${RUNTIME_DIR}/el_runtime.c" \
+            -lcurl -lpthread -o "${out_bin}" 2>/tmp/text_test.cc.err; then
+        echo "FAIL  ${name} — cc failed:"
+        cat /tmp/text_test.cc.err | sed 's/^/      /'
+        FAIL=$((FAIL+1))
+        FAILED_NAMES+=("${name}")
+        rm -f "${out_c}" "${out_bin}"
+        return
+    fi
+
+    local got
+    got="$("${out_bin}" 2>&1)"
+
+    if [ "${got}" = "${expected}" ]; then
+        echo "PASS  ${name}"
+        PASS=$((PASS+1))
+    else
+        echo "FAIL  ${name}  expected: '${expected}', got: '${got}'"
+        FAIL=$((FAIL+1))
+        FAILED_NAMES+=("${name}")
+    fi
+
+    rm -f "${out_c}" "${out_bin}"
+}
+
+echo "==> Running text-primitives acceptance corpus"
+echo
+
+run_runtime_case "count-substring"          examples/count-substring.el          "3"
+run_runtime_case "count-overlap-skip"       examples/count-overlap-skip.el       "2"
+run_runtime_case "count-lines-words-letters" examples/count-lines-words-letters.el "2/4/22"
+run_runtime_case "index-of-all"             examples/index-of-all.el             "2,5,8"
+run_runtime_case "transform-suite"          examples/transform-suite.el          "ababab|olleh|bar|hello|hello"
+run_runtime_case "char-classes"             examples/char-classes.el             "true"
+run_runtime_case "split-lines"              examples/split-lines.el              "3"
+run_runtime_case "join"                     examples/join.el                     "alpha, beta, gamma"
+
+echo
+echo "${PASS} passed, ${FAIL} failed"
+if [ "${FAIL}" -gt 0 ]; then
+    echo "failed: ${FAILED_NAMES[*]}"
+    exit 1
+fi
+exit 0