feat: add Codex CLI provider for subprocess integration (#80)

* feat: add Codex CLI provider for OpenAI subprocess integration

Add CodexCliProvider that wraps `codex exec --json` as a subprocess,
analogous to the existing ClaudeCliProvider pattern. This enables using
OpenAI's Codex CLI tool as a local LLM backend.

- CodexCliProvider: subprocess wrapper parsing JSONL event stream
- Credential reader for ~/.codex/auth.json with token expiry detection
- Factory integration: provider "codex-cli" and auth_method "codex-cli"
- Fix tilde expansion in workspace path for CLI providers
- 37 unit tests covering parsing, prompt building, credentials, and mocks

* fix: add tool call extraction to Codex CLI provider

- Extract shared tool call parsing into tool_call_extract.go
  (extractToolCallsFromText, stripToolCallsFromText, findMatchingBrace)
- Both ClaudeCliProvider and CodexCliProvider now share the same
  tool call extraction logic for PicoClaw-specific tools
- Fix cache token accounting: include cached_input_tokens in total
- Add 2 new tests for tool call extraction from JSONL events
- Update existing tests for corrected token calculations

* fix(docker): update Go version to match go.mod requirement

Dockerfile used golang:1.24-alpine but go.mod requires go >= 1.25.7.
This caused Docker builds to fail on all branches with:
  "go: go.mod requires go >= 1.25.7 (running go 1.24.13)"

Update to golang:1.25-alpine to match the project requirement.

* fix: handle codex CLI stderr noise without losing valid stdout

Codex writes diagnostic messages to stderr (e.g. rollout errors) which
cause non-zero exit codes even when valid JSONL output exists on stdout.
Parse stdout first before checking exit code to avoid false errors.

* style: fix gofmt formatting and update web search API in tests

- Remove trailing whitespace in web.go and base_test.go
- Update config_test.go and web_test.go for WebSearchToolOptions API

pkg/providers/claude_cli_provider.go

@@ -171,68 +171,14 @@ func (p *ClaudeCliProvider) parseClaudeCliResponse(output string) (*LLMResponse,
 	}, nil
 }
 
-// extractToolCalls parses tool call JSON from the response text.
+// extractToolCalls delegates to the shared extractToolCallsFromText function.
 func (p *ClaudeCliProvider) extractToolCalls(text string) []ToolCall {
-	start := strings.Index(text, `{"tool_calls"`)
-	if start == -1 {
-		return nil
-	}
-
-	end := findMatchingBrace(text, start)
-	if end == start {
-		return nil
-	}
-
-	jsonStr := text[start:end]
-
-	var wrapper struct {
-		ToolCalls []struct {
-			ID       string `json:"id"`
-			Type     string `json:"type"`
-			Function struct {
-				Name      string `json:"name"`
-				Arguments string `json:"arguments"`
-			} `json:"function"`
-		} `json:"tool_calls"`
-	}
-
-	if err := json.Unmarshal([]byte(jsonStr), &wrapper); err != nil {
-		return nil
-	}
-
-	var result []ToolCall
-	for _, tc := range wrapper.ToolCalls {
-		var args map[string]interface{}
-		json.Unmarshal([]byte(tc.Function.Arguments), &args)
-
-		result = append(result, ToolCall{
-			ID:        tc.ID,
-			Type:      tc.Type,
-			Name:      tc.Function.Name,
-			Arguments: args,
-			Function: &FunctionCall{
-				Name:      tc.Function.Name,
-				Arguments: tc.Function.Arguments,
-			},
-		})
-	}
-
-	return result
+	return extractToolCallsFromText(text)
 }
 
-// stripToolCallsJSON removes tool call JSON from response text.
+// stripToolCallsJSON delegates to the shared stripToolCallsFromText function.
 func (p *ClaudeCliProvider) stripToolCallsJSON(text string) string {
-	start := strings.Index(text, `{"tool_calls"`)
-	if start == -1 {
-		return text
-	}
-
-	end := findMatchingBrace(text, start)
-	if end == start {
-		return text
-	}
-
-	return strings.TrimSpace(text[:start] + text[end:])
+	return stripToolCallsFromText(text)
 }
 
 // findMatchingBrace finds the index after the closing brace matching the opening brace at pos.