fix(web_search): align with CONVENTION.md var ordering and function order

[devproje]

What this changes

A convention pass over the just-merged #78 found violations of docs/CONVENTION.md in modules/web_search/web_search.go and its test:

• braveSearch/tavilySearch/ollamaSearch declared results before hit, but hit is what the for _, hit = range ... loop actually assigns first each iteration — results is only touched inside the loop body afterward.
• formatResults declared body before index/result, but the for index, result = range results assigns those first; body.WriteString only happens after.
• formatResults itself was defined above the three backend functions even though Search's Execute calls it only after (and outside) the backend dispatch switch — CONVENTION.md wants helpers ordered by when their caller actually invokes them.
• Two test functions had the same first-use-order issue (lookup/wantErr, got/results).

How it was verified

• make test-race passes
• New behaviour has a test, or there is nothing to test — pure reordering, no behavior change, existing tests cover it

Checklist

• Follows docs/CONVENTION.md: no comments, no :=, one var block per function in first-use order with err last, callees before callers, and main unconditionally last
• New .go files carry the two-line SPDX header
• Documentation updated if behaviour a user can see has changed (none — no behavior change)
• My contribution is licensed GPL-3.0-only, matching the project