docs: sync cross-referenced metrics with code truth

[google-labs-jules]

Fixes drift in AGENTS.md, README.md, and docs-canonical/TEST-SPEC.md where metrics counts (extractors, sink classes, test suite size, and proof score) had become outdated after recent additions (e.g. dependencies extractor, log-injection sink).

What:

• Bumps extractor count from 20 -> 22
• Bumps sink classes count from 16 -> 17
• Bumps test suite count from 285 -> 324
• Fixes websec proof proxy score from 10/10 -> 8/10

Why:
To satisfy docguard guard and ensure Canonical-Driven Development truthfulness. The actual codebase metrics were confirmed via shell scripts and unittest.

Risk:
None. Documentation only. Codebase semantics are untouched.

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PR created automatically by Jules for task 12380112041996765686 started by @raccioly

[google-labs-jules]

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