deps: bump api-client-go to v0.13.3

[steve-calvert-glean]

Pure dependency bump: brings in the platform API namespaces (Search, Agents on /api/* routes) and the WithIncludeExperimental SDK option needed for the platform-first migration. Classic client surface unchanged — zero code churn, snapshots untouched.

Discovery notes for the stack (verified from SDK source):

• Hidden 404 for gated experimental endpoints surfaces as PlatformProblemDetailError{Status:404, Code:resource_not_found} or generic APIError 404 — no dedicated gating code or header visible to clients.
• PlatformSearchRequest supports query, page_size, cursor, datasources, datasource_instances, filters, time_range.
• Agents.CreateRun takes agent_id as a path parameter, separate from the body.

Part 1/9 of the platform-API migration stack (sc/platform-01 → 10).

🤖 Generated with Claude Code

[steve-calvert-glean]

• feat(skills): reframe generated skill as thin router to agent-help #139
• feat(agent-help): self-describing usage command for coding agents #138
• feat(agenthelp): runtime agent-doc collection from the cobra tree #137
• feat(agents): serve agents commands from the platform API by default #136
• feat(cmdutil): teach Build the platform-first fallback protocol #135
• feat(search): serve glean search from the platform API by default #134
• feat(search): platform search request builder and runner #133
• feat(platform): platform-first routing with legacy fallback #132
• deps: bump api-client-go to v0.13.3 #131 👈 (View in Graphite)
• main

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