feat(arsenal): subdomain takeover detection built-in (#134)

* feat(arsenal): add subdomain-takeover classifier + fingerprint table

Pure, I/O-free detection logic split into src/arsenal/takeover.ts so it is fully
unit-testable without DNS or network:
- TAKEOVER_FINGERPRINTS: curated CNAME + unclaimed-resource-body signatures for 15
  high-frequency services (S3, GitHub Pages, Heroku, Azure, Fastly, Shopify, Netlify, ...)
- classifySubdomainTakeover(): conservative verdict (confirmed / potential / none) driven by
  a dangling CNAME and/or a service body fingerprint; no cross-service false matches
- renderTakeoverReport(): human-readable output block

* feat(arsenal): register subdomain_takeover_check built-in + bump tool count 108->109

- New keyless, self-contained built-in tool 'subdomain_takeover_check' (recon): resolves the
  CNAME, checks whether the target still resolves (dangling), fetches the live body via the
  scope-gated targetFetch, and classifies via classifySubdomainTakeover. Emits a real finding.
- Added to the Recon operator's default toolkit so the swarm can reach it (operator-toolkits
  coverage invariant).
- Bumped the advertised arsenal size 108 -> 109 in lockstep across the count-honesty test,
  README, and verify-claims (73 adapters + 36 built-in).

* test(arsenal): cover subdomain_takeover_check (classifier matrix + mocked DNS/fetch e2e)

- classifySubdomainTakeover decision matrix: confirmed via body fingerprint, confirmed via
  dangling nxdomain-prone CNAME, potential (known service, no confirmation), potential
  (dangling unknown), none (no CNAME / resolves clean), and no cross-service false matching
- renderTakeoverReport output shape
- end-to-end handler test with DNS + fetch mocked, driving the confirmed S3 path

README.md

@@ -191,7 +191,7 @@ The framework is an 8-operator kill chain, and this table won't blow smoke about
 | Re-derivable measurement (`verify-claims`) | ✅ Stable | every headline recomputes from committed artifacts |
 | Recon engine | ✅ Stable | drives nmap / DNS / HTTP / fingerprinting; every finding traces to real tool output |
 | Mission engine + War Room + Op Admiral | ✅ Stable | keyless through a connected local agent |
-| Arsenal, MCP server, HTTP API | ✅ Stable | 35 built-in tools by default; 108 with the opt-in `T3MP3ST_FULL_ARSENAL` (+73 adapters, with dangerous/catalog-only drivers — metasploit, hydra, pacu, frida — behind narrow approved paths rather than generic execution) — both counts re-derive via `verify-claims`. `security_recon` over MCP |
+| Arsenal, MCP server, HTTP API | ✅ Stable | 36 built-in tools by default; 109 with the opt-in `T3MP3ST_FULL_ARSENAL` (+73 adapters, with dangerous/catalog-only drivers — metasploit, hydra, pacu, frida — behind narrow approved paths rather than generic execution) — both counts re-derive via `verify-claims`. `security_recon` over MCP |
 | Egress-scope containment | ✅ Stable (on by default) | once a mission target is set, built-in networked tools refuse off-scope public hosts — not the target/subdomains, not loopback/private (`SCOPE DENIED`) — a tightened default, not a bare tool runner |
 | Coordinated-disclosure pipeline | ✅ Stable | OSV novelty + live PoC + refuter panel + CVSS; drafts only, a human sends |
 | White-box source analysis | ⚠️ Experimental | Multi-language ingest via web-tree-sitter (Python/JS/TS/Go/Java/C/C++); Python retains its regex parser, while other languages fail open to no extracted blocks; multi-model decomposition costs more tokens, not fewer |