fix: address all review findings (zero remaining)

Tests:
- Add WithTemperature tests (builder method, chaining, zero omission)
- Add temperature serialization tests (omitted when 0, included when set)

Composite action:
- Use python3 for robust JSON version parsing (replaces sed)
- Verify SHA-256 checksum before executing downloaded binary
- Wire up repo input (no longer hardcodes rodin/review-bot)

Release workflow:
- Handle 409 conflict (existing release for tag)
- Use file-based JSON parsing for reliability

Code:
- Tighten WithTemperature doc comment (single clear line)
- Fix flag alignment (missing tab on llmTemp declaration)

llm/client.go

@@ -28,10 +28,7 @@ func NewClient(baseURL, apiKey, model string) *Client {
 	}
 }
 
-// WithTemperature sets the temperature for LLM requests.
-// A value of 0 (the zero value) means the field is omitted from the request,
-// causing the server to use its default temperature.
-// If not set (zero value), the server default is used.
+// WithTemperature sets the temperature for LLM requests (0 = omit, uses server default).
 func (c *Client) WithTemperature(t float64) *Client {
 	c.Temperature = t
 	return c