refactor: server-side user prompt construction with @pullfrog tag check (#123)

- Move prompt construction logic from action-side to server-side (webhook handler and trigger page)
- Include issue/comment body in USER PROMPT only if @pullfrog was tagged (checked server-side using containsTriggerPhrase)
- Add repoInstructions as separate REPO-LEVEL INSTRUCTIONS section in FULL prompt
- Macro-expand repoInstructions server-side before sending to action
- Trigger page never includes body (manual triggers)
- Remove redundant customInstructions field (now combined into prompt server-side)

files changed:
- action/external.ts: add repoInstructions to WriteablePayload, remove customInstructions
- action/utils/payload.ts: add repoInstructions to JsonPayload schema, remove customInstructions
- action/utils/repoSettings.ts: add repoInstructions to RepoSettings interface
- action/utils/instructions.ts: use payload.prompt directly, add repo section to full prompt, add repo field to ResolvedInstructions
- utils/webhooks/handleWebhook.ts: check @pullfrog tag and include body if tagged, macro-expand repoInstructions
- app/trigger/[owner]/[repo]/[number]/page.tsx: macro-expand repoInstructions (never include body)

utils/instructions.ts

@@ -63,6 +63,7 @@ export interface ResolvedInstructions {
   full: string;
   system: string;
   user: string;
+  repo: string;
   event: string;
   runtime: string;
 }
@@ -82,8 +83,12 @@ export function resolveInstructions(ctx: InstructionsContext): ResolvedInstructi
 
   const runtime = buildRuntimeContext(ctx);
 
+  // user prompt is constructed server-side (body if @pullfrog tagged + per-trigger instructions)
   const user = ctx.payload.prompt;
 
+  // repo-level instructions are macro-expanded server-side and passed separately
+  const repo = ctx.payload.repoInstructions ?? "";
+
   const userQuoted = user
     .split("\n")
     .map((line) => `> ${line}`)
@@ -163,12 +168,22 @@ After selecting a mode, follow the detailed step-by-step instructions provided b
 
 Eagerly inspect the MCP tools available to you via the \`${ghPullfrogMcpName}\` MCP server. These are VITALLY IMPORTANT to completing your task.`;
 
+  // build repo instructions section (only if non-empty)
+  const repoSection = repo
+    ? `
+
+************* REPO-LEVEL INSTRUCTIONS *************
+
+${repo}`
+    : "";
+
   const full = `
 ${system}
 
 ************* USER PROMPT *************
 
 ${userQuoted}
+${repoSection}
 
 ************* EVENT DATA *************
 
@@ -180,5 +195,5 @@ ${event}
 
 ${runtime}`;
 
-  return { full, system, user, event, runtime };
+  return { full, system, user, repo, event, runtime };
 }