fix(httpd): treat forced shutdown as a successful stop

[AllBeingsFuture]

Problem

When graceful http.Server.Shutdown times out (common with long-lived SSE streams), the daemon forced Close() and then returned an error. That made the process exit 1. Electron surfaced intentional stop/restart as "daemon start failed" (code: exited) even though the user/app asked to stop.

Solution

After shutdown timeout + forced close, log and return <-serveErr (normally nil after ErrServerClosed) instead of wrapping the timeout as a failure. Forced close is still an intentional, successful stop.

Tests

• go test ./internal/httpd/ -count=1
• Existing lifecycle / POST /shutdown tests still expect a nil Run error on intentional stop.

Notes

• Backend-only product fix extracted from local desktop WIP (local/zh-ui-sync). Independent of any Chinese UI branch — no i18n or frontend changes.
• Does not include the staged migration renumber (0025 → 0029); that is owned by fix(storage): renumber duplicate migration 0025 to 0029 #3014.
• CI may stay red on main if migrate panics on the duplicate 0025 until fix(storage): renumber duplicate migration 0025 to 0029 #3014 merges; this PR does not depend on that renumber.

Independence

Can merge independently of the tmux and workspace product fixes.

[somewherelostt]

Thanks for contributing to Agent Orchestrator.

This PR is being picked up by the current external contributor on-call pair:

• @illegalcall
• @Pulkit7070

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