fix(prompts): make --fgm override OCO_EMOJI config

getCommitConvention gated the entire GitMoji branch on
config.OCO_EMOJI, so --fgm was silently ignored unless the user had
previously run `oco config set OCO_EMOJI true`. Since OCO_EMOJI
defaults to false, --fgm was a no-op for most users.

This violates the standard CLI convention that command-line flags
should override configuration. Restructure getCommitConvention so
that --fgm forces FULL_GITMOJI_SPEC regardless of OCO_EMOJI:

  --fgm=true                    → FULL_GITMOJI_SPEC
  --fgm=false + OCO_EMOJI=true  → GITMOJI_HELP (unchanged)
  --fgm=false + OCO_EMOJI=false → CONVENTIONAL_COMMIT_KEYWORDS (unchanged)

No other files need changes — the fgm flag was already threaded
correctly through cli.ts → commit.ts → generateCommitMessageByDiff
→ getMainCommitPrompt → getCommitConvention.

src/prompts.ts

@@ -95,11 +95,11 @@ const CONVENTIONAL_COMMIT_KEYWORDS =
   'Do not preface the commit with anything, except for the conventional commit keywords: fix, feat, build, chore, ci, docs, style, refactor, perf, test.';
 
 const getCommitConvention = (fullGitMojiSpec: boolean) =>
-  config.OCO_EMOJI
-    ? fullGitMojiSpec
-      ? FULL_GITMOJI_SPEC
-      : GITMOJI_HELP
-    : CONVENTIONAL_COMMIT_KEYWORDS;
+  fullGitMojiSpec
+    ? FULL_GITMOJI_SPEC
+    : config.OCO_EMOJI
+      ? GITMOJI_HELP
+      : CONVENTIONAL_COMMIT_KEYWORDS;
 
 const getDescriptionInstruction = () =>
   config.OCO_DESCRIPTION