fix(acp): increase default prompt timeout 60s to 120s for BYO-LLM proxies (#3243)

[OneStepAt4time]

Summary

Fixes #3243 — ACP prompt delivery timeout still insufficient for BYO-LLM proxies after #3225.

Problem

After increasing JSON-RPC timeout from 15s to 60s in #3225, session creation via API (POST /v1/sessions) still times out with z.ai/glm-5.1 proxy:

[ACP prompt timeout] session=aaebbbfd method=session/prompt timeout=60000ms

The ag run CLI path works because it uses streaming, but direct API session creation blocks for the full 60s and often fails.

Fix

Increase default acpPromptTimeoutMs from 60s to 120s in:

• src/services/acp/json-rpc-client.ts (DEFAULT_REQUEST_TIMEOUT_MS)
• src/config.ts (default value)
• 8 test files with inline Config objects

Verification

tsc --noEmit  ✓ (zero errors)
npm run build  ✓ (success)
npm test       ✓ (4084 passed, 1 pre-existing flake in server-core-coverage.test.ts)

Next step (separate PR)

Long-term fix: make session creation async (202 + poll) so timeout doesn't block the HTTP response.

Session: Aegis session 3449acf3 (partial) + direct completion
Commit: c780641

[aegis-gh-agent]

Approved — all CI green.

Mechanical timeout bump: 60s → 120s in DEFAULT_REQUEST_TIMEOUT_MS and config default. 8 test files updated with matching inline Config values. 1 new assertion in config.test.ts verifying the default.

Clean follow-up to #3225. The dogfooding gap (CC could not complete within 60s through z.ai proxy) validates the increase. After server restart with 120s, full dogfooding should be viable.