fix: cross-platform CA trust (Arch/Fedora + Windows) (#41)

* fix: cross-platform CA trust (Arch/Fedora + Windows)

Closes #35.

trust_ca_linux now detects which trust store the distro ships and
runs the matching refresh command, instead of hardcoding Debian's
update-ca-certificates. Detection walks a const table in priority
order, picking the first whose anchor dir exists:

  - debian: /usr/local/share/ca-certificates  (update-ca-certificates)
  - pki:    /etc/pki/ca-trust/source/anchors  (update-ca-trust extract)
  - p11kit: /etc/ca-certificates/trust-source/anchors (trust extract-compat)

Falls back with a clear error listing every backend tried.

Adds Windows support via certutil -addstore Root / -delstore Root,
removing the silent CA-trust gap on numa install (previously the
service installed but the trust step quietly errored, leaving every
HTTPS .numa request throwing browser warnings).

Refactor: trust_ca and untrust_ca are now thin dispatchers calling
per-platform helpers. CA_COMMON_NAME and CA_FILE_NAME are centralized
in tls.rs and reused from system_dns.rs and api.rs. untrust_ca_linux
no longer pre-checks file existence (TOCTOU) and skips the refresh
when no file was actually removed.

Test: tests/docker/install-trust.sh runs the install/uninstall
contract against debian:stable, fedora:latest, and archlinux:latest
in containers, asserting the cert lands in (and is removed from)
the system bundle. All three pass locally.

README notes the Firefox/NSS limitation (separate trust store).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* style: rustfmt fixes for trust_ca_linux helpers

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* test: macOS CA trust contract test (manual)

Adds tests/manual/install-trust-macos.sh — a sudo bash script that
mirrors trust_ca_macos / untrust_ca_macos against a fixture cert with
a unique CN. Designed to coexist with a running production numa:

- Refuses to run if a real "Numa Local CA" is already in System.keychain
  (fail-closed protection for dogfood installs)
- Uses a unique CN ("Numa Local CA Test <pid-timestamp>") so the test
  cert can never collide with production
- Mirrors the by-hash deletion loop from untrust_ca_macos
- Trap-cleanup on success or interrupt

Lives under tests/manual/ to signal "host-mutating, dev-only" — distinct
from tests/docker/install-trust.sh which is hermetic.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* test: relax bail-out in macOS trust test (safe alongside production)

The bail-out was overly defensive. The test cert uses a unique CN
("Numa Local CA Test <pid-ts>") that is strictly longer than the
production CN, so `security find-certificate -c $TEST_CN` cannot
substring-match the production cert. All deletes are by-hash, which
can only target the test cert's specific hash. Coexistence is
provably safe; document the reasoning in the header comment block
and replace the refusal with an informational notice.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/tls.rs

@@ -13,6 +13,13 @@ use time::{Duration, OffsetDateTime};
 const CA_VALIDITY_DAYS: i64 = 3650; // 10 years
 const CERT_VALIDITY_DAYS: i64 = 365; // 1 year
 
+/// Common Name on Numa's local CA. Referenced by trust-store helpers
+/// (`security`, `certutil`) when locating the cert for removal.
+pub const CA_COMMON_NAME: &str = "Numa Local CA";
+
+/// Filename of the CA certificate inside the data dir.
+pub const CA_FILE_NAME: &str = "ca.pem";
+
 /// Collect all service + LAN peer names and regenerate the TLS cert.
 pub fn regenerate_tls(ctx: &ServerCtx) {
     let tls = match &ctx.tls_config {
@@ -67,7 +74,7 @@ pub fn build_tls_config(
 
 fn ensure_ca(dir: &Path) -> crate::Result<(rcgen::Certificate, KeyPair)> {
     let ca_key_path = dir.join("ca.key");
-    let ca_cert_path = dir.join("ca.pem");
+    let ca_cert_path = dir.join(CA_FILE_NAME);
 
     if ca_key_path.exists() && ca_cert_path.exists() {
         let key_pem = std::fs::read_to_string(&ca_key_path)?;
@@ -86,7 +93,7 @@ fn ensure_ca(dir: &Path) -> crate::Result<(rcgen::Certificate, KeyPair)> {
     let mut params = CertificateParams::default();
     params
         .distinguished_name
-        .push(DnType::CommonName, "Numa Local CA");
+        .push(DnType::CommonName, CA_COMMON_NAME);
     params.is_ca = IsCa::Ca(BasicConstraints::Unconstrained);
     params.key_usages = vec![KeyUsagePurpose::KeyCertSign, KeyUsagePurpose::CrlSign];
     params.not_before = OffsetDateTime::now_utc();