v1.38.0 — Security and availability hardening

Read HARDENING.md before upgrading. This release follows the
project's pre-2.0 minor-version convention but includes breaking changes.

Breaking

• Signing keys must contain at least 32 UTF-8 bytes and eight distinct
  characters. Generate a random key; existing weak configurations fail startup.
  The explicit public development key now binds launchers to loopback only.
• IP-bound tokens use a domain-separated HMAC over the canonical address.
  Older tokens fail remoteip checks with new validators: drain old instances
  and their five-minute tokens before switching the validation pool.
• Browser network failures now reject instead of creating local challenges or
  unsigned tokens. An empty API URL means same origin. Manual integrations must
  handle rejection; automatic forms remain on the page and report the error.
• Node requires version 22 or later; Go builds require 1.26.8.
• Public APIs enforce bounded admission: 20,000 requests globally and 600 per
  source per minute, with 60 challenge requests per source per minute. Backend
  verification requests also share their source's allowance. Check proxy trust
  and shared-egress capacity before deployment. Security-state exhaustion denies
  new work rather than evicting live challenges or replay protection.

Security and reliability

• Bound challenge issuance/storage, spent-token retention, rate state, Web Bot
  Auth discovery/cache/concurrency, response sizes, and outbound connections.
  Redis admission and challenge quotas are atomic across replicas.
• Add Redis-aware /ready, bounded Node command deadlines/queueing, and
  coalesced readiness probes. /health remains independent process liveness.
• Remove the fast-JavaScript detector from all runtimes: normal fast hardware
  is not evidence of automation. Benchmark results are explicitly regression
  evidence, not population-level accuracy measurements.
• Release shared browser listeners on teardown, preserve form submission
  semantics, and cap proof-of-work workers at four.
• Update vulnerable dependencies; hash-lock Python dependencies; pin container
  bases and run as non-root; add dependency automation and image provenance/SBOMs.
• Extend admission, outage, lifecycle, cross-runtime, and browser regression
  checks. Correct the npm diagnostic workflow and browser CI server ownership.

Subresource Integrity

{
  "version": "1.38.0",
  "fcaptcha.js": "sha384-fJ4VZCz/51CKORMKLiAZp+12G1Jx+gnaJLClk/xRadq4M31tcOKYMVUkJIgO5r66",
  "dist/fcaptcha.min.js": "sha384-FzxXKVB7W9Si2+PBe+XrI9o4opSZBk4MNLbTpn0Vle3Cs6MgEggUbdBfk7aDEl9d"
}

Validated by all 18 checks in #53.