fix: Detect calling agent via env vars and centralize agent config (#418)

* fix: detect calling agent via env vars for correct badge display

Add prioritized agent detection chain: CODEX_THREAD_ID (codex) >
COPILOT_CLI (copilot-cli) > default (claude-code). All subcommands
use the shared detectedOrigin constant. Display name updated from
'Copilot CLI' to 'GitHub Copilot'. TypeScript origin union type
updated to include 'copilot-cli'.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* refactor: centralize agent config into @plannotator/shared/agents

- Create packages/shared/agents.ts as single source of truth for Origin type,
  agent display names (AGENT_CONFIG), getAgentName(), and getAgentBadge()
- Replace all inline origin type unions across 8 files with Origin import
- Type detectedOrigin and ServerOptions.origin as Origin for compile-time safety
- Add @plannotator/shared dependency to @plannotator/editor package.json
- Adding a new agent is now a one-file change to AGENT_CONFIG

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: restore gitContext in startReviewServer call

Accidentally removed alongside the origin refactor. Without it, local
code reviews lose branch detection, diff-type switching, and CWD resolution.

For provenance purposes, this commit was AI assisted.

---------

Co-authored-by: Yecats <Yecats@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Michael Ramos <mdramos8@gmail.com>

packages/server/review.ts

@@ -10,6 +10,7 @@
  */
 
 import { isRemoteSession, getServerPort } from "./remote";
+import type { Origin } from "@plannotator/shared/agents";
 import { type DiffType, type GitContext, runGitDiff, getFileContentsForDiff, gitAddFile, gitResetFile, parseWorktreeDiffType, validateFilePath } from "./git";
 import { getRepoInfo } from "./repo";
 import { handleImage, handleUpload, handleAgents, handleServerReady, handleDraftSave, handleDraftLoad, handleDraftDelete, handleFavicon, type OpencodeClient } from "./shared-handlers";
@@ -39,7 +40,7 @@ export interface ReviewServerOptions {
   /** HTML content to serve for the UI */
   htmlContent: string;
   /** Origin identifier for UI customization */
-  origin?: "opencode" | "claude-code" | "pi";
+  origin?: Origin;
   /** Current diff type being displayed */
   diffType?: DiffType;
   /** Git context with branch info and available diff options */