Clarify lazy-mode deferred-login message

[ChrisJBurns]

Summary

Follow-up to #5427 addressing review feedback (comment).

The thv llm setup --lazy message told the user they'd be "signed in automatically the first time a configured tool accesses the LLM gateway". As @jerm-dro noted, "signed in automatically" isn't quite accurate — the deferred login still opens a browser for the user to complete on the first request. This rewords the message so it accurately describes when login happens.

Before:

Lazy mode: skipping OIDC login. You'll be signed in automatically
the first time a configured tool accesses the LLM gateway.

After:

Lazy mode: skipping OIDC login. You'll be signed in on the first
request a configured tool makes to the LLM gateway.

Type of change

• Documentation (user-facing message wording; no behavior change)

Test plan

• Unit tests (task test) — pkg/llm, cmd/thv/app pass (updated the lazy-message assertion in setup_test.go)
• task build passes
• Manual: thv llm setup --lazy prints the reworded message

Does this introduce a user-facing change?

Yes — the wording of the thv llm setup --lazy informational message changes. No behavior change.

Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.85%. Comparing base (6ebadaf) to head (261bab5).

Additional details and impacted files

@@ Coverage Diff @@## main #5429 +/- ##
==========================================
- Coverage 68.86% 68.85% -0.02% 
==========================================
Files 634 634 Lines 64437 64437 ==========================================
- Hits 44377 44369 -8 - Misses 16782 16791 +9 + Partials 3278 3277 -1 

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