Feat/btoa uri pbkdf2

[cs01]

feat: btoa/atob, encodeURIComponent, crypto.pbkdf2

Adds several Web API globals and a key derivation primitive: btoa/atob, encodeURIComponent/decodeURIComponent, and crypto.pbkdf2. Includes a new uri-bridge.c for percent-encoding, docs for all new APIs plus URL/URLSearchParams (merged separately), and CI fixes for artifact packaging and cross-compile reliability.

What's new

btoa / atob

const encoded = btoa("hello world");  // "aGVsbG8gd29ybGQ="
const decoded = atob(encoded);        // "hello world"

const auth = "Basic " + btoa(username + ":" + password);

encodeURIComponent / decodeURIComponent

const q = encodeURIComponent("hello world & foo=bar");
// "hello%20world%20%26%20foo%3Dbar"

const url = "https://api.example.com/search?q=" + encodeURIComponent(userInput);

RFC 3986 compliant — only unreserved chars (A-Z a-z 0-9 - _ . ~) are left unencoded.

crypto.pbkdf2(password, salt, iterations, keylen)

const key = crypto.pbkdf2(userPassword, randomSalt, 100000, 32);
// 64-char hex string (32 bytes)

Uses OpenSSL PKCS5_PBKDF2_HMAC with SHA-256. Known test vector: pbkdf2("password", "salt", 1, 20) → "0c60c80f961f0e71f3a9b524af6012062fe037a6".

Implementation

• c_bridges/base64-bridge.c — added cs_btoa and cs_atob to existing base64 bridge. Handles standard base64 with padding.
• c_bridges/uri-bridge.c (new) — cs_encode_uri_component and cs_decode_uri_component using GC-aware allocation.
• src/codegen/expressions/calls.ts — dispatch for btoa, atob, encodeURIComponent, decodeURIComponent as global functions (same pattern as parseInt/isNaN).
• src/codegen/stdlib/crypto.ts — generatePbkdf2 using OpenSSL PKCS5 PBKDF2 HMAC.

CI fixes

• scripts/build-target-sdk.sh — add uri-bridge.o to cross-compile SDK tarball.
• .github/workflows/ci.yml — add uri-bridge.o to all 4 artifact locations (Linux verify, Linux release, macOS verify, macOS release). Also add --target-cpu=x86-64 to stage0 compilation so native code doesn't use AVX/newer instructions that crash GitHub's baseline x86-64 runners.
• tests/self-hosting.test.ts — pass --target-cpu=x86-64 to stage0 build.

Docs

• docs/stdlib/encoding.md (new) — btoa/atob, encodeURIComponent/decodeURIComponent
• docs/stdlib/crypto.md — added crypto.pbkdf2 section
• docs/stdlib/url.md (new) — URL and URLSearchParams (feature landed in add url and urlsearchparams classes with c bridge #107, docs here)
• docs/stdlib/index.md — updated globals example