feat(registry): ?verification_mode and ?verified filters for GET /api/registry/agents

[bokelley]

Closes #3505

docs/building/aao-verified.mdx#registry-filter has advertised verification-mode filtering on the federated agent listing since PR #2153, but GET /api/registry/agents never wired up the parameter. This PR closes that gap.

What changed

Two new optional query parameters on GET /api/registry/agents:

Param	Accepted values	Behavior
?verification_mode	spec, live (repeat for AND)	Filter to agents whose active badge covers all listed axes
?verified	true	Filter to agents with any active verification badge

Both params are additive: ?verified=true&verification_mode=live requires a badge covering live (the withVerified check is then a strict subset of the verificationModes check, so no redundancy).

Filter semantics — AND across repeated params, via a single-badge predicate:

badges.some(b =>
  modesOk  // badge.verification_modes ⊇ requested_modes
  && verifiedOk  // badge.verification_modes non-empty (if ?verified=true)
)

Validation — unknown verification_mode values get a 400 with valid_values: ["spec","live"].

Error handling — DB failure returns 503 (not silently unfiltered, which would leak unverified agents to callers who asked for verified-only).

Badge map reuse — when ?compliance=true is also set, the badge map fetched for the filter is reused in the enrichment step (saves one round-trip).

bySource counts now reflect the filtered agent set (previously always reflected the full unfiltered listing).

Non-breaking justification

Both params are optional. Callers that omit them hit the unchanged listAllAgents + early-return path (if (!withHealth && !withCapabilities...)) with no behavioral change.

Pre-PR review

• code-reviewer: approved after fixes — three blockers resolved: (1) combined withVerified+verificationModes predicate, (2) z.enum(["true"]) consistent with sibling params, (3) 503 on badge-fetch failure
• adtech-product-expert: approved — AND semantics correct for current single-badge data model; naming ?verified + ?verification_mode natural for buyers

Triage-managed PR. This bot does not currently iterate on
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See #3121
for context.

Session: https://claude.ai/code/session_01K5MAwn6xWdaQLNP4hf1sCy

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