feat: Windows DNS configuration via netsh (#28)

* feat: Windows DNS configuration via netsh

numa install/uninstall now set/restore system DNS on Windows via
netsh. Parses ipconfig /all per-interface (adapter name, DHCP status,
DNS servers), saves backup to %APPDATA%\numa\original-dns.json, and
restores on uninstall (DHCP or static with secondary servers).

Handles localization (German adapter/DHCP/DNS labels), disconnected
adapters, multiple interfaces, and missing admin privileges. Adds IP
validation to discover_windows() for consistency.

No Windows Service or CA trust yet — user runs numa in a terminal.

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

* ci: add cargo test to Windows CI job

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

* ci: upload Windows binary as artifact for testing

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

* fix: SRTT decay tests panic on Windows due to Instant underflow

On Windows, Instant starts near boot time — subtracting large
durations panics. Use checked_sub with a process-start fallback.

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

* fix: SRTT decay tests use binary search for max Instant age

Replace age() helper with set_age_secs() on SrttCache that
binary-searches for the maximum subtractable duration. Prevents
panic on Windows (Instant starts at boot) while still producing
the oldest representable instant for correct decay calculations.

Also removes ephemeral test-ubuntu.sh from git.

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

* fix: use ProgramData for Windows DNS backup path

APPDATA differs between user and admin contexts — install runs as
admin but uninstall might resolve a different APPDATA. Use
ProgramData which is consistent across elevation contexts.

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

* feat: disable Dnscache on Windows install, re-enable on uninstall

Windows DNS Client (Dnscache) holds port 53 at kernel level and
can't be stopped via sc/net stop. Disable via registry during
install (requires reboot), re-enable on uninstall.

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

* fix: rewrite SRTT decay tests as pure functions

Decay tests manipulated Instant timestamps which panics on Windows
(Instant can't go before boot time). Rewrite to test decay_for_age()
directly — a pure function taking srtt_ms and age_secs, no platform
dependency.

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

* fix: use Quad9 IP (9.9.9.9) for DoH fallback, not hostname

DoH to dns.quad9.net requires DNS to resolve the hostname, which
creates a chicken-and-egg loop when numa IS the system resolver
(e.g. after numa install on Windows). Using the IP directly avoids
the bootstrap dependency.

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

* refactor: extract DOH_FALLBACK constant

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

* refactor: extract QUAD9_IP constant

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

* refactor: remove dead test helpers, fix constant placement

Remove unused get_srtt_ms() and saturated_penalty_cache() left over
from SRTT test rewrite. Move QUAD9_IP/DOH_FALLBACK after use block.

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

* fix: ignore ConnectionReset on UDP socket (Windows ICMP error)

Windows delivers ICMP port-unreachable as ConnectionReset on the
next UDP recv_from, crashing numa. Linux/macOS silently ignore these.
Catch and continue the recv loop.

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

* feat: auto-start numa on Windows boot via registry Run key

Without a Windows Service, rebooting after numa install leaves DNS
broken (pointing at 127.0.0.1 with nothing listening). Register
numa in HKLM\...\Run so it starts automatically. Removed on
uninstall.

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

* docs: update README, Windows plan, and launch drafts for Windows support

- README: platform-specific Quick Start, install/uninstall table
- Windows plan: Phase 2 complete, Phase 3 scoped
- Launch drafts: updated "Does it support Windows?" response

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

* chore: remove docs from git tracking (already gitignored)

docs/ is in .gitignore but files were force-added. Remove from
tracking — files remain on disk.

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

---------

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

README.md

@@ -15,16 +15,32 @@ Built from scratch in Rust. Zero DNS libraries. RFC 1035 wire protocol parsed by
 ## Quick Start
 
 ```bash
+# macOS
 brew install razvandimescu/tap/numa
-# or: cargo install numa
-# or: curl -fsSL https://raw.githubusercontent.com/razvandimescu/numa/main/install.sh | sh
 
-sudo numa                              # port 53 requires root
+# Linux
+curl -fsSL https://raw.githubusercontent.com/razvandimescu/numa/main/install.sh | sh
+
+# Windows — download from GitHub Releases
+# All platforms
+cargo install numa
+```
+
+```bash
+sudo numa                              # run in foreground (port 53 requires root/admin)
 ```
 
 Open the dashboard: **http://numa.numa** (or `http://localhost:5380`)
 
-Set as system DNS: `sudo numa install`
+Set as system DNS:
+
+| Platform | Install | Uninstall |
+|----------|---------|-----------|
+| macOS | `sudo numa install` | `sudo numa uninstall` |
+| Linux | `sudo numa install` | `sudo numa uninstall` |
+| Windows | `numa install` (admin) + reboot | `numa uninstall` (admin) + reboot |
+
+On macOS and Linux, numa runs as a system service (launchd/systemd). On Windows, numa auto-starts on login via registry.
 
 ## Local Services
 
@@ -80,7 +96,7 @@ From Machine B: `curl http://api.numa` → proxied to Machine A's port 8000. Ena
 | Ad blocking | Yes | Yes | — | 385K+ domains |
 | Web admin UI | Full | Full | — | Dashboard |
 | Encrypted upstream (DoH) | Needs cloudflared | Yes | — | Native |
-| Portable (laptop) | No (appliance) | No (appliance) | Server | Single binary |
+| Portable (laptop) | No (appliance) | No (appliance) | Server | Single binary, macOS/Linux/Windows |
 | Community maturity | 56K stars, 10 years | 33K stars | 20 years | New |
 
 ## Performance