Add a connector declaration snapshot

[jif-oai]

Why

Connector declarations currently enter Codex through broad plugin capability summaries, then MCP setup, turn tooling, and app/list each reconstruct the same information. That makes executor-selected connectors difficult to add without coupling connector behavior to the host plugin loader.

This PR introduces a small connector-owned value that later stack layers can populate before thread startup.

What changed

• Move the pure app-declaration parser into codex-connectors, preserving declaration order and category cleanup while leaving host-side validation and deduplication unchanged.
• Add an immutable ConnectorSnapshot with ordered connector IDs and plugin display-name provenance.
• Adapt the existing local-plugin capability summaries into that snapshot at current consumer boundaries.
• Use the snapshot for MCP tool provenance, turn connector inventory, and app/list.
• Keep the crate API narrow: no test-only snapshot accessors are exposed.

The externally visible behavior is unchanged. Connector tools still come from the orchestrator-owned /ps/mcp server, and local plugin enablement remains owned by the existing plugin loader.

Stack scope

This is the foundation only. It does not read selected executor packages or change thread startup. #29852 adds the executor-backed declaration reader, and #29856 composes selected declarations into a thread snapshot.

[chatgpt-codex-connector]

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