feat: forward-by-default, auto recursive mode, Linux install fixes (#27)

* feat: auto recursive mode, fix Linux install

Auto mode (new default): probes a root server on startup; uses
recursive resolution if outbound DNS works, falls back to Quad9 DoH
if blocked. Dashboard shows mode indicator (green/yellow).

Linux install fixes:
- Add DNSStubListener=no to resolved drop-in (frees port 53)
- Configure DNS before starting service (correct ordering)
- Skip 127.0.0.53 in upstream detection
- `numa install` now does everything (service + DNS + CA)
- `numa uninstall` mirrors install (stop service + restore DNS)
- Extract is_loopback_or_stub() for consistent filtering

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: enable DNSSEC validation by default

With recursive as the default mode, DNSSEC validation completes the
trustless resolution chain. Strict mode remains off by default.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: forward search domains to VPC resolver on Linux

Parse search/domain lines from resolv.conf and create conditional
forwarding rules to the original nameserver or AWS VPC resolver
(169.254.169.253). Fixes internal hostname resolution on cloud VMs
where recursive mode can't resolve private DNS zones.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: single-pass resolv.conf parsing, eliminate redundancies

Parse resolv.conf once for both upstream and search domains instead
of 2-3 reads. Extract CLOUD_VPC_RESOLVER constant. Use &'static str
for mode in StatsResponse. Remove dead read_upstream_from_file.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: macOS install health check, harden recursive probe

Verify numa is listening (API port) before redirecting system DNS on
macOS — if the service fails to start (e.g. port 53 in use), unload
the service and abort instead of breaking DNS. Probe up to 3 root
hints before declaring recursive mode unavailable. Validate IPs from
resolvectl to avoid IPv6 fragment extraction. Extract DEFAULT_API_PORT
constant.

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

* fix: widen make_rule cfg gate to include Linux

make_rule was gated to macOS-only but discover_linux() calls it for
search domain forwarding rules. CI failed on Linux with E0425.

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

* feat: forward mode as default, recursive opt-in

Forward mode (transparent proxy to system DNS) is now the default.
Recursive and auto modes are explicit opt-in via config. This avoids
bypassing corporate DNS policies, captive portals, VPC private zones,
and parental controls on first install.

- Move #[default] from Auto to Forward on UpstreamMode
- DNSSEC defaults to off (no-op in forward mode)
- 3-way match in main: Forward/Recursive/Auto with clean separation
- Post-install message suggests mode = "recursive" for sovereignty
- Update README, site, and launch drafts messaging

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

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

site/index.html

@@ -4,10 +4,10 @@
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>Numa — DNS you own. Everywhere you go.</title>
-<meta name="description" content="DNS you own. Recursive resolver with full DNSSEC validation, ad blocking, .numa local domains, developer overrides. A single portable binary built from scratch in Rust.">
+<meta name="description" content="DNS you own. Portable DNS resolver with caching, ad blocking, .numa local domains, developer overrides. Optional recursive resolution with full DNSSEC validation. Built from scratch in Rust.">
 <link rel="canonical" href="https://numa.rs">
 <meta property="og:title" content="Numa — DNS you own. Everywhere you go.">
-<meta property="og:description" content="Recursive DNS resolver with full DNSSEC validation, ad blocking, .numa local domains, and developer overrides. Built from scratch in Rust.">
+<meta property="og:description" content="Portable DNS resolver with caching, ad blocking, .numa local domains, and developer overrides. Optional recursive resolution with full DNSSEC validation. Built from scratch in Rust.">
 <meta property="og:type" content="website">
 <meta property="og:url" content="https://numa.rs">
 <link rel="stylesheet" href="/fonts/fonts.css">
@@ -1232,17 +1232,17 @@ footer .closing {
     <div class="reveal">
       <div class="section-label">How It Works</div>
       <h2>What it does today</h2>
-      <p class="lead">A recursive DNS resolver with DNSSEC validation, ad blocking, local service domains, and a REST API. Everything runs in a single binary.</p>
+      <p class="lead">A DNS resolver with caching, ad blocking, local service domains, and a REST API. Optional recursive resolution with DNSSEC. Everything runs in a single binary.</p>
     </div>
     <div class="layers-grid">
       <div class="layer-card reveal reveal-delay-1">
         <div class="layer-badge">Layer 1</div>
         <h3>Resolve &amp; Protect</h3>
         <ul>
-          <li>Recursive resolution &mdash; resolve from root nameservers, no upstream needed</li>
-          <li>DNSSEC validation &mdash; chain-of-trust + NSEC/NSEC3 denial proofs (RSA, ECDSA, Ed25519)</li>
+          <li>Forward mode by default &mdash; transparent proxy to your existing DNS, with caching</li>
           <li>Ad &amp; tracker blocking &mdash; 385K+ domains, zero config</li>
-          <li>DNS-over-HTTPS &mdash; encrypted upstream as alternative to recursive mode</li>
+          <li>Recursive resolution &mdash; opt-in, resolve from root nameservers, no upstream needed</li>
+          <li>DNSSEC validation &mdash; chain-of-trust + NSEC/NSEC3 denial proofs (RSA, ECDSA, Ed25519)</li>
           <li>TTL-aware caching (sub-ms lookups)</li>
           <li>Single binary, portable &mdash; macOS, Linux, and Windows</li>
         </ul>