feat(ttp): extract intel_lifter provider mappings to YAML data + ATT&CK external_reference enrichment

The four provider→technique tables (AbuseIPDB cat→techniques,
GreyNoise tag→techniques, ThreatFox threat_type→techniques, plus
the Feodo binary-listed signal) used to live as Final[dict] constants
in intel_lifter.py. Two real problems with that:

1. Drift between rules/ttp/R0054.yaml..R0058.yaml (which declare
   the full slate per provider) and the Python dicts (which decide
   which slate-member fires per signal). The v2 audit comment in
   intel_lifter.py documented that they had silently drifted.
2. No ATT&CK provenance on emissions — the loaded STIX bundle has
   rich external_references (canonical attack.mitre.org URLs) that
   never surfaced because the lifter had no path back to them.

Mappings now live as YAML at decnet/ttp/data/intel/{provider}.yaml,
validated at load against the loaded ATT&CK bundle, with each entry
enriched by attack_stix._attack_pattern_by_id to attach the canonical
MITRE URL to every emission.

- decnet/ttp/data/intel_loader.py: pydantic-validated schema +
  ProviderMapping/Signal/TechniqueEmission frozen dataclasses +
  load_provider_mapping(provider) lru-cached.
- Per-technique high_score_threshold inlined into YAML
  (collapses the separate _ABUSEIPDB_HIGH_SCORE_GATED dict).
- external_reference field follows the STIX 2.1 external-reference
  shape (source_name + url + optional external_id) so the future
  STIX/MISP exporter is a direct translation.
- intel_lifter.py: dicts deleted, decision functions read from
  ProviderMapping accessors. Decision-flow constants (T1071/T1595
  bare-classification fallbacks in _greynoise_decisions) stay in
  code — they're not table rows.
- Each emit slot's evidence_extra now carries mitre_url for any
  technique resolved in the bundle (every one in practice).
- tests/ttp/test_intel_mappings.py: snapshot equivalence vs the
  legacy dicts, high-score gate behavior, every-signal-has-an-
  external-reference, every-emission-has-a-mitre-url, negative
  paths (unknown technique_id raises AttackBundleError, mismatched
  provider field rejected, dir listing matches expected providers).

The YAML schema + mitre_url enrichment lays groundwork for the
future STIX exporter; this commit does NOT build that exporter.

decnet/ttp/data/intel/greynoise.yaml

@@ -0,0 +1,74 @@
+# GreyNoise tag → ATT&CK technique mapping.
+#
+# Mirrors what _GREYNOISE_TAG_TO_TECHNIQUES used to encode in
+# decnet/ttp/impl/intel_lifter.py. Note: GreyNoise's Community
+# endpoint does not return tags; these fire only when operators wire
+# a non-Community provider (Visualizer / Enterprise / RIOT). Kept
+# canonical here so the upgrade path is a column populate, not a
+# code change. Decision-flow constants for bare ``classification ==
+# "scanner"`` (T1595) and bare ``classification == "malicious"``
+# (T1071 at 0.5×) stay in code — they're not table rows.
+provider: greynoise
+mapping_version: "1"
+attack_release: ">=15.1"
+signals:
+  - id: tor_exit_node
+    label: "Tor exit node"
+    external_reference:
+      source_name: greynoise
+      url: "https://docs.greynoise.io/docs/understanding-greynoise-tags"
+      external_id: tor_exit_node
+    techniques:
+      - technique_id: T1090
+  - id: ssh_bruteforcer
+    label: "SSH brute-forcer"
+    external_reference:
+      source_name: greynoise
+      url: "https://docs.greynoise.io/docs/understanding-greynoise-tags"
+      external_id: ssh_bruteforcer
+    techniques:
+      - technique_id: T1110
+  - id: web_crawler
+    label: "Web crawler"
+    external_reference:
+      source_name: greynoise
+      url: "https://docs.greynoise.io/docs/understanding-greynoise-tags"
+      external_id: web_crawler
+    techniques:
+      - technique_id: T1595
+  - id: cobalt_strike
+    label: "Cobalt Strike"
+    external_reference:
+      source_name: greynoise
+      url: "https://docs.greynoise.io/docs/understanding-greynoise-tags"
+      external_id: cobalt_strike
+    techniques:
+      - technique_id: T1071
+      - technique_id: T1588
+  - id: metasploit
+    label: "Metasploit"
+    external_reference:
+      source_name: greynoise
+      url: "https://docs.greynoise.io/docs/understanding-greynoise-tags"
+      external_id: metasploit
+    techniques:
+      - technique_id: T1071
+      - technique_id: T1588
+  - id: sliver
+    label: "Sliver"
+    external_reference:
+      source_name: greynoise
+      url: "https://docs.greynoise.io/docs/understanding-greynoise-tags"
+      external_id: sliver
+    techniques:
+      - technique_id: T1071
+      - technique_id: T1588
+  - id: havoc
+    label: "Havoc"
+    external_reference:
+      source_name: greynoise
+      url: "https://docs.greynoise.io/docs/understanding-greynoise-tags"
+      external_id: havoc
+    techniques:
+      - technique_id: T1071
+      - technique_id: T1588