fix(providers): omit temperature for Claude Opus/Sonnet 4.6+

[ojusave]

Anthropic returns HTTP 400 when temperature is sent to claude-opus-4-6, claude-sonnet-4-6, and newer 4.x models. Agent summoning and chat both hardcode temperature; skip the field for affected model IDs.

Summary

Omit temperature from Anthropic Messages API request bodies when the model is Claude Opus/Sonnet 4.6 or newer. Summoning (temperature: 0.7 in summoner_regenerate.go) and chat paths both flow through buildRequestBody; filtering at the provider adapter fixes both without changing every call site.

Type

• Feature
• Bug fix
• Hotfix (targeting main)
• Refactor
• Docs
• CI/CD

Target Branch

dev

Checklist

• go build ./... passes
• go build -tags sqliteonly ./... passes (if Go changes)
• go vet ./... passes
• Tests pass: go test -race ./...
• Web UI builds: cd ui/web && pnpm build (if UI changes) — N/A, no UI changes
• No hardcoded secrets or credentials
• SQL queries use parameterized $1, $2 (no string concat) — N/A, no SQL changes
• New user-facing strings added to all 3 locales (en/vi/zh) — N/A, no new strings
• Migration version bumped in internal/upgrade/version.go (if new migration) — N/A, no migration

Test Plan

• Added TestAnthropicAdapterToRequest_SkipsTemperatureForClaude46: asserts temperature is omitted for claude-opus-4-6, claude-sonnet-4-6, and claude-opus-4-7-*, and still sent for claude-sonnet-4-5-20250929.
• Ran go build ./..., go build -tags sqliteonly ./..., go vet ./..., and go test -race ./... locally; all pass.
• Manual repro (pre-fix): agent summoning with claude-opus-4-6 returned Anthropic 400 (temperature is deprecated for this model). Post-fix: request omits temperature and summoning succeeds.