chore(release): 0.9.6 -- atomic init + Windows one-command installer

[ArkNill]

Summary

Surfaced by the 2026-05-21 hmj PC dogfood: llm-relay init would write
ANTHROPIC_BASE_URL into ~/.claude/settings.json before the proxy
server was confirmed serving traffic, so any running Claude Code session
would route to a dead port and the symptom looked like a generic API
connection error. This release fixes the ordering and adds a one-line
Windows installer on top.

User-visible deliverable:

irm https://raw.githubusercontent.com/ArkNill/llm-relay/main/scripts/install.ps1 | iex

That's the whole install (after Python 3.9+ is present).

What changed

llm-relay init is now atomic

Step	Before	After
1	detect / port / DB / config / knowledge	same
2	write ANTHROPIC_BASE_URL → settings.json	start the proxy server
3	start proxy server	/_health gate
4	health-check (but routing already mutated)	write ANTHROPIC_BASE_URL + register MCP only if step 3 passed

--skip-server now also skips the routing change as one decision; the
previous trap of "server skipped, settings still mutated" is gone.

Windows daemon path

_start_server on Windows delegates to win_service.start_daemon (pythonw +
CREATE_BREAKAWAY_FROM_JOB). The previous Popen + CREATE_NEW_PROCESS_GROUP
path left the proxy tied to its job object, so the OS killed it when the
parent SSH session disconnected (observed during the 2026-05-21 dogfood).

scripts/install.ps1 -- one-command Windows install

• Verifies Python 3.9+ (or exits with a winget install hint linking to the
  README Prerequisites section).
• Detects an active venv (uses it if present, else --user with a PATH hint).
• pip install --upgrade "llm-relay[all]".
• Calls llm-relay init.
• Prints dashboard URL.

README

New "Prerequisites" section spelling out Python 3.9+, recommended venv flow,
and platform-specific install hints. New "One-command install (Windows native)"
section at the top of Install pointing at install.ps1.

Tests

test_skip_server_does_not_write_settings_json regression in
tests/test_api/test_init.py pins the atomic contract: with
skip_server=True, settings.json must remain untouched.

Docker carry-over

CHANGELOG carries forward the 0.9.5 Docker fix that landed via PR #24
(Dockerfile vendor/tokpress lines removed).

Test plan

• pytest -- 594 pass (+1 new atomic regression). 0 fail.
• ruff check src/ tests/ -- clean.
• NDA grep on diff -- 0 hits.
• Manual trace through the new ordering with a dead port (would-be
  failure path) confirms settings.json is not touched when health gate
  fails.

Post-merge sequence

1. git tag v0.9.6 + push.
2. gh release create v0.9.6 with CHANGELOG body.
3. gh workflow run publish.yml -f confirm=publish (Trusted Publishing OIDC).
4. Dogfood install.ps1 from hmj PC: fresh PowerShell,
   irm https://raw.githubusercontent.com/ArkNill/llm-relay/main/scripts/install.ps1 | iex,
   confirm verify all passes and Claude Code's existing session is not
   disrupted mid-flow.