feat(creds): Phase 1 — Authorization header + SNMP community capture

Closes the cred-coverage gap for 7 services that already had the data
on the wire but never landed it in the Credential table:

- SNMP — community string lands as secret_kind="snmp_community",
  principal=None (v1/v2c has no per-user identity, the community IS
  the auth).
- SIP — Digest response hash, previously buried in the auth= header
  dump, now classify_authorization()-extracted.
- HTTP / HTTPS — Authorization header was in the headers JSON but
  never extracted. Now Basic decodes to plaintext, Bearer →
  http_bearer (principal=None), Digest → http_digest_md5.
- K8s — already extracted Authorization but didn't normalize. Service-
  account JWTs flow through as Bearer.
- Docker API — headers absent entirely. Adds the headers JSON dump
  and runs Authorization through the classifier.
- Elasticsearch — five distinct request handlers; each gains a
  per-handler _cred_fields() helper.

Adds canonical templates/syslog_bridge.py:classify_authorization().
Recognised: Basic / Bearer / Token / Digest. Unknown schemes (NTLM,
AWS4-HMAC, Negotiate) return None; the header still rides in the
ambient SD-block but isn't normalized as a credential. The SD shape
on the wire collapses sip_digest_md5 into http_digest_md5 — same
algorithm, so cross-protocol reuse correlates correctly when (rare)
nonce collisions allow.

Drive-by repair of tests/core/test_fingerprinting.py:

- The pre-existing `test_http_useragent_extracted` asserted both that
  add_bounty was called exactly once AND that the UA payload carried
  `path` and `method` fields. Both wrong since this session opened:
  the http_quirks fingerprint added later fires too, and the UA
  payload never actually included path/method despite the assertion.
- Adds `path`/`method` to the UA fingerprint payload (real operator
  value: "Nikto hit /admin" beats "Nikto seen on this decky").
- Replaces `assert_awaited_once` with a `_find_ua_bounty()` helper
  that filters add_bounty calls by `fingerprint_type`. New fingerprint
  families landing later won't retroactively break old tests.
- Updates the two credential-bearing tests to use the post-DEBT-039
  native shape (`secret_b64` / `principal`) and `upsert_credential`,
  not the deleted legacy `username+password` adapter.

Also rebuilds the per-service fake `syslog_bridge` modules in
tests/service_testing/{conftest,test_imap,test_pop3,test_snmp,test_mqtt,test_smtp}.py
to expose `encode_secret` + `classify_authorization`. Service templates
that import either now no longer fail at test collection.

173 tests pass in the touched scope. Phases 2-7 still pending.

decnet/templates/https/syslog_bridge.py

@@ -12,8 +12,10 @@ RFC 5424 structure:
 Facility: local0 (16). SD element ID uses PEN 55555.
 """
 
+import base64
+import re
 from datetime import datetime, timezone
-from typing import Any
+from typing import Any, Optional
 
 # ─── Constants ────────────────────────────────────────────────────────────────
 
@@ -79,6 +81,106 @@ def syslog_line(
     return f"{pri}1 {ts} {host} {appname} {_NILVALUE} {msgid} {sd}{message}"
 
 
+def encode_secret(secret: str) -> dict[str, str]:
+    """Standardized credential-secret encoding for the universal SD-block shape.
+
+    Returns ``{'secret_printable': ..., 'secret_b64': ...}`` ready to spread
+    into a :func:`syslog_line` / ``_log`` call::
+
+        _log("auth_attempt", principal=user, **encode_secret(password))
+
+    ``secret_printable`` mirrors auth-helper.c's sd_escape: bytes outside
+    ``[0x20, 0x7f)`` collapse to ``'?'`` so the field is always parser-safe
+    RFC 5424 ASCII. ``secret_b64`` preserves the *original* utf-8 bytes —
+    NUL/0xff/control/non-utf8 sequences all survive losslessly, useful as
+    a fingerprinting signal even when the printable form sanitizes them.
+
+    The decnet web ingester's native-shape branch keys off ``secret_b64``
+    being present, so any service emitter calling this helper lands its
+    cred attempt directly in the :class:`Credential` table.
+    """
+    raw = secret.encode("utf-8", errors="replace")
+    printable = "".join(chr(b) if 0x20 <= b < 0x7f else "?" for b in raw)
+    return {
+        "secret_printable": printable,
+        "secret_b64": base64.b64encode(raw).decode("ascii"),
+    }
+
+
+_DIGEST_PARAM_RE = re.compile(r'(\w+)\s*=\s*"([^"]*)"|(\w+)\s*=\s*([^,\s]+)')
+
+
+def classify_authorization(header_value: Optional[str]) -> Optional[dict[str, Any]]:
+    """Parse an HTTP Authorization header value into Credential SD fields.
+
+    Returns a dict with the universal cred shape ready to spread into a
+    ``_log(...)`` call::
+
+        auth = request.headers.get("Authorization")
+        cred = classify_authorization(auth)
+        if cred:
+            _log("auth_attempt", **cred)
+
+    Recognised schemes:
+      * Basic — base64(user:pw); decoded → ``principal=user`` +
+        ``secret_kind="plaintext"`` + ``encode_secret(pw)``.
+      * Bearer / Token — opaque token; ``principal=None`` +
+        ``secret_kind="http_bearer"`` + ``encode_secret(token)``.
+      * Digest — ``principal=username`` from header +
+        ``secret_kind="http_digest_md5"`` + ``encode_secret(response)``.
+
+    Returns ``None`` for anything unrecognized (AWS4-HMAC-SHA256, NTLM,
+    Negotiate, …) — callers can still log the raw header value in the
+    ambient SD-block; we just don't know how to extract a hashable
+    secret from it.
+    """
+    if not header_value or not isinstance(header_value, str):
+        return None
+    parts = header_value.strip().split(None, 1)
+    if len(parts) < 2:
+        return None
+    scheme, rest = parts[0].lower(), parts[1].strip()
+
+    if scheme == "basic":
+        try:
+            decoded = base64.b64decode(rest, validate=True).decode("utf-8", errors="replace")
+        except (ValueError, base64.binascii.Error):
+            return None
+        if ":" not in decoded:
+            return None
+        user, _, pw = decoded.partition(":")
+        return {
+            "principal": user,
+            "secret_kind": "plaintext",
+            **encode_secret(pw),
+        }
+
+    if scheme in ("bearer", "token"):
+        return {
+            "principal": None,
+            "secret_kind": "http_bearer",
+            **encode_secret(rest),
+        }
+
+    if scheme == "digest":
+        params: dict[str, str] = {}
+        for m in _DIGEST_PARAM_RE.finditer(rest):
+            k = m.group(1) or m.group(3)
+            v = m.group(2) if m.group(2) is not None else m.group(4)
+            if k:
+                params[k.lower()] = v
+        response = params.get("response")
+        if not response:
+            return None
+        return {
+            "principal": params.get("username"),
+            "secret_kind": "http_digest_md5",
+            **encode_secret(response),
+        }
+
+    return None
+
+
 def write_syslog_file(line: str) -> None:
     """Emit a syslog line to stdout for container log capture."""
     print(line, flush=True)