fix(federation): address #494 review findings (FED-M2-04)

H1: Replace HS256/HMAC signing with real JWK signing (ES256/RS256/ES384)
    via jose SignJWT. Algorithm derived from JWK kty/crv. Provisioner
    password dropped as signing input; kept only as optional env var for
    PBES2-decrypt path at startup.
H2: Clamp cert TTL to 900s (15 min) in both DTO validator and issueCert().
    Default changed to 300s (5 min). @Max reduced to 15*60.
H3: Real CSR validation via @peculiar/x509: parse PEM, verify self-
    signature, reject weak keys (RSA<2048, bad EC curves), reject MD5/SHA-1.
    New validateCsr() throws CaServiceError code INVALID_CSR on failure.
H4: Replace hardcoded \x24 DER length in federation.tpl with dynamic
    printf "%c" (len ...) encoding. Add UUID-shape validation for grantId
    and subjectUserId in buildOtt() with code INVALID_GRANT_ID.
H5: Load JWK into KeyObject once (lazy, cached). provisionerKeyJson raw
    string not stored as class field. provisionerPassword not stored.

M1: Set JWT sub to CSR CN (extracted via @peculiar/x509) instead of URL.
M2: Add jti: crypto.randomUUID() to OTT claims.
M3: Drop top-level sha claim; keep only step.sha.
M4: extractSerial() throws CaServiceError code CERT_PARSE instead of
    returning 'unknown' on failure.
M5: Set timeout: 5000 on https.RequestOptions + req.setTimeout(5000).
M6: OTT signature verified with jose.jwtVerify in tests. Added real P-256
    CSR test via @peculiar/x509 generator. Added provisionerPassword
    leak-check test.
M7: Constructor validates STEP_CA_URL must be https://.

Verification: typecheck ✓, 385 tests pass (16 new), lint ✓, format ✓.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

infra/step-ca/templates/federation.tpl

@@ -39,12 +39,12 @@
     {
       "id": "1.3.6.1.4.1.99999.1",
       "critical": false,
-      "value": "{{ printf "\x0c\x24%s" .Token.mosaic_grant_id | b64enc }}"
+      "value": "{{ printf "\x0c%c%s" (len .Token.mosaic_grant_id) .Token.mosaic_grant_id | b64enc }}"
     },
     {
       "id": "1.3.6.1.4.1.99999.2",
       "critical": false,
-      "value": "{{ printf "\x0c\x24%s" .Token.mosaic_subject_user_id | b64enc }}"
+      "value": "{{ printf "\x0c%c%s" (len .Token.mosaic_subject_user_id) .Token.mosaic_subject_user_id | b64enc }}"
     }
   ],