Add CockroachDB error-based fingerprints (PostgreSQL fork)

CockroachDB is already recognized as a PostgreSQL fork by the active
fingerprint, but data/xml/errors.xml had no passive (error-message)
signatures for it, so error-based detection couldn't flag a CockroachDB
backend the way it does for the existing MySQL forks (MariaDB/TiDB/MemSQL).

Add two CockroachDB-specific error signatures under the PostgreSQL block:
  - the location-first syntax error ('at or near "...": syntax error',
    distinct from PostgreSQL's 'syntax error at or near ...')
  - the go.crdb.dev / github.com/cockroachdb reference link emitted in
    CockroachDB error hints

Validated against CockroachDB v26.2 (Docker): htmlParser() resolves these
to PostgreSQL with forkNote='CockroachDB', while genuine PostgreSQL/MySQL
errors and unrelated pages are unaffected (no false attribution). Each
signature carries a CockroachDB-specific token to avoid false positives.
sha256sums.txt regenerated; smoke test passes.

Author: potato-20

data/txt/sha256sums.txt

@@ -77,7 +77,7 @@ a7eb4d1bcbdfd155383dcd35396e2d9dd40c2e89ce9d5a02e63a95a94f0ab4ea  data/xml/banne
 e2febc92f9686eacf17a0054f175917b783cc6638ca570435a5203b03245fc18  data/xml/banner/x-aspnet-version.xml
 3a440fbbf8adffbe6f570978e96657da2750c76043f8e88a2c269fe9a190778c  data/xml/banner/x-powered-by.xml
 0223157364ea212de98190e7c6f46f9d2ee20cf3d17916d1af16e857bb5dc575  data/xml/boundaries.xml
-bc23e6213d55390661da57ca7424b3d9876062015cf8f5b66717157bdd3895ea  data/xml/errors.xml
+0678220c8659b8bedfdb5753f0d527a3258643bd74b3484c3f7e323c3bbb08ed  data/xml/errors.xml
 d0b094a110bccec97d50037cc51445191561c0722ec53bf2cebe1521786e2451  data/xml/payloads/boolean_blind.xml
 53d0f29459f37248c320d5cb9960d432f46889696d27ae30cc3a3309fd6e026c  data/xml/payloads/error_based.xml
 b0f434f64105bd61ab0f6867b3f681b97fa02b4fb809ac538db382d031f0e609  data/xml/payloads/inline_query.xml

data/xml/errors.xml

@@ -34,6 +34,8 @@
         <error regexp="org\.postgresql\.jdbc"/>
         <error regexp="Pdo[./_\\]Pgsql"/>
         <error regexp="PSQLException"/>
+        <error regexp="at or near &quot;[^&quot;]*&quot;: syntax error" fork="CockroachDB"/>
+        <error regexp="See: https?://(go\.crdb\.dev|github\.com/cockroachdb)" fork="CockroachDB"/>
     </dbms>
 
     <dbms value="Microsoft SQL Server">