Replace go-openai with native client

Drop the github.com/sashabaranov/go-openai dependency in favor of an
internal HTTP client.

The LLM package is now split into:
- llm.go: type definitions (Message, ChatRequest, ChatResponse, etc.)
- client.go: client construction and configuration
- client_completions.go: Completions and CompletionsStream methods
- client_models.go: ListModels
- client_tools.go: tool call execution

CompletionsStream uses typed SSE events (delta, done, message) so the
frontend can render progressive streaming output.

Move tool.go and tool_test.go from internal/tool/ into internal/llm/
to co-locate the registry with the client that consumes it.

Update job.go and service.go to use the new llm.Message types and
Completions/CompletionsStream methods. Remove the Voice field from
chat request/response (voice is now tracked via message metadata).

Frontend: handle delta/done/message SSE events, render a streaming
placeholder that receives progressive text deltas, and finalize with
full message binding (reasoning, tool calls, actions).

internal/job/job.go

@@ -13,7 +13,6 @@ import (
 	"time"
 
 	"github.com/robfig/cron/v3"
-	"github.com/sashabaranov/go-openai"
 
 	"code.chimeric.al/chimerical/odidere/internal/config"
 	"code.chimeric.al/chimerical/odidere/internal/llm"
@@ -124,7 +123,7 @@ type Result struct {
 	Duration time.Duration
 	// Messages is the full conversation returned by the LLM agent loop,
 	// including tool calls and tool results. Empty if the job failed.
-	Messages []openai.ChatCompletionMessage
+	Messages []llm.Message
 	// Error is set if the job failed.
 	Error error
 }
@@ -138,10 +137,15 @@ func (j *Job) Run(ctx context.Context) Result {
 	log.Info("starting job")
 
 	// Build messages from job config.
-	messages := []openai.ChatCompletionMessage{
+	messages := []llm.Message{
 		{
-			Role:    openai.ChatMessageRoleUser,
-			Content: j.Task(),
+			Role: llm.RoleUser,
+			ContentParts: []llm.ContentPart{
+				{
+					Text: j.Task(),
+					Type: llm.ContentTypeText,
+				},
+			},
 		},
 	}
 
@@ -152,12 +156,12 @@ func (j *Job) Run(ctx context.Context) Result {
 		defer cancel()
 	}
 
-	msgs, err := j.llm.Query(
+	msgs, err := j.llm.Completions(
 		ctx,
-		messages,
 		j.model,
 		j.SystemMessage(),
 		j.MaxIterations(),
+		messages,
 	)
 
 	duration := time.Since(start)