feat: add diagram reads

[AlexanderNZ]

I added the diagram read endpoints so MCP can list and fetch diagrams, plus thumbnails.

What I changed

• added list/get diagram reads
• added list/get diagram thumbnail reads
• added formatting for diagram output

Why I did it

• diagrams are core to the architecture model, but were missing from MCP reads

Notes

• depends on the refactor in PR refactor: remove teams support and harden tests #23

Test plan

• not run

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Note

Medium Risk
Moderate risk due to introducing a new, large IcePanel API client surface (env-configured base URL, timeouts/retries, error handling) and wiring new MCP tools to new endpoints; regressions could affect all API calls and tool outputs.

Overview
Adds a new icepanel-client service that centralizes authenticated IcePanel API calls, including timeout/retry logic, base URL validation via env vars, and user-facing handleApiError messaging, plus many new read/write endpoint wrappers.

Introduces new MCP tools in diagrams.ts to list/get diagrams and diagram thumbnails, including optional fuzzy search, pagination, and markdown/json formatting, and wires them into registerAllTools.

Updates types.ts to expand model object enums and add response/request types for connections, model-object/tag/domain write operations, and diagram/thumbnail payloads (and removes the old Team/TeamsResponse types).

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Recommended merge order

• PR refactor: reduce filter param duplication #19 (filter refactor)
• PR feat: add HTTP transport (Streamable HTTP) #20 (HTTP transport)
• PR feat: add Docker support #21 (Docker support)
• PR feat: add IcePanel write tools #22 (write tools)
• PR refactor: remove teams support and harden tests #23 (refactor + tests)
• PR feat: add tag and tag group reads #24 (tags + tag groups)
• PR feat: add domain reads #25 (domains)
• PR feat: add connection reads #26 (connections)
• PR feat: add diagram reads #27 (diagrams)
• PR feat: add flow reads #28 (flows)
• PR feat: add model object export reads #29 (model object exports)
• PR docs: expand read tools and tests #30 (docs + tests)