Normalize escaped multiline issue and approval text (#4444)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - The board and agent APIs accept multiline issue, approval,
interaction, and document text
> - Some callers accidentally send literal escaped newline sequences
like `\n` instead of JSON-decoded line breaks
> - That makes comments, descriptions, documents, and approval notes
render as flattened text instead of readable markdown
> - This pull request centralizes multiline text normalization in shared
validators
> - The benefit is newline-preserving API behavior across issue and
approval workflows without route-specific fixes

## What Changed

- Added a shared `multilineTextSchema` helper that normalizes escaped
`\n`, `\r\n`, and `\r` sequences to real line breaks.
- Applied the helper to issue descriptions, issue update comments, issue
comment bodies, suggested task descriptions, interaction summaries,
issue documents, approval comments, and approval decision notes.
- Added shared validator regressions for issue and approval multiline
inputs.

## Verification

- `pnpm exec vitest run --project @paperclipai/shared
packages/shared/src/validators/approval.test.ts
packages/shared/src/validators/issue.test.ts`
- `pnpm --filter @paperclipai/shared typecheck`

## Risks

- Low risk. This only changes text fields that are explicitly multiline
user/operator content.
- If a caller intentionally wanted literal backslash-n text in these
fields, it will now render as a real line break.

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- OpenAI Codex, GPT-5 coding agent, tool-enabled with
shell/GitHub/Paperclip API access. Context window was not reported by
the runtime.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

packages/shared/src/validators/approval.ts

@@ -1,5 +1,6 @@
 import { z } from "zod";
 import { APPROVAL_TYPES } from "../constants.js";
+import { multilineTextSchema } from "./text.js";
 
 export const createApprovalSchema = z.object({
   type: z.enum(APPROVAL_TYPES),
@@ -11,13 +12,13 @@ export const createApprovalSchema = z.object({
 export type CreateApproval = z.infer<typeof createApprovalSchema>;
 
 export const resolveApprovalSchema = z.object({
-  decisionNote: z.string().optional().nullable(),
+  decisionNote: multilineTextSchema.optional().nullable(),
 });
 
 export type ResolveApproval = z.infer<typeof resolveApprovalSchema>;
 
 export const requestApprovalRevisionSchema = z.object({
-  decisionNote: z.string().optional().nullable(),
+  decisionNote: multilineTextSchema.optional().nullable(),
 });
 
 export type RequestApprovalRevision = z.infer<typeof requestApprovalRevisionSchema>;
@@ -29,7 +30,7 @@ export const resubmitApprovalSchema = z.object({
 export type ResubmitApproval = z.infer<typeof resubmitApprovalSchema>;
 
 export const addApprovalCommentSchema = z.object({
-  body: z.string().min(1),
+  body: multilineTextSchema.pipe(z.string().min(1)),
 });
 
 export type AddApprovalComment = z.infer<typeof addApprovalCommentSchema>;