Reduce spurious Copilot Code Review comments on AutoPR PRs (#38768)

## Problem

Copilot Code Reviewer (CCR) generates noisy, repetitive, or unactionable
comments on auto-generated ARM SDK PRs. Observed in:
- #38603
- #38664

**Examples:**
- 12+ identical comments about subscriptionId placeholder format across
every sample file
- Comments on \pnpm-lock.yaml\ specifier mismatches (not actionable)
- Comments on generated config files (\eslint.config.mjs\,
\warp.config.yml\) deviating from other packages

## Changes

- **\.github/copilot-instructions.md\** — Add repo-wide review behavior
rules: deduplicate comments, skip lockfile, recognize \[AutoPR\ title
prefix
- **\.github/instructions/reviewer/mgmt-sdk.instructions.md\** — Add
rules to skip placeholder values in samples, generated infrastructure
config files, and duplicate comments
- **\.github/instructions/reviewer/lockfile.instructions.md\** (new) —
Path-scoped exclusion for \pnpm-lock.yaml\

## Verification

These changes will take effect on new PRs after merge. Effectiveness can
be validated by observing comment patterns on subsequent AutoPR PRs.

---------

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

Author: xirzec

.github/copilot-instructions.md

@@ -113,15 +113,24 @@ When possible, refer to the Azure SDK for JS Design Guidelines for specific exam
 ## Local SDK Generation and Package Lifecycle (TypeSpec)
 
 ### AUTHORITATIVE REFERENCE
+
 For all TypeSpec-based SDK workflows (generation, building, validation, testing, versioning, and release preparation), follow #file:../eng/common/instructions/azsdk-tools/local-sdk-workflow.instructions.md
 
 ### DEFAULT BEHAVIORS
+
 - **Repository:** Use the current workspace as the local SDK repository unless the user specifies a different path.
 - **Configuration:** Identify `tsp-location.yaml` from files open in the editor. If unclear, ask the user.
 
 ### REQUIRED CONFIRMATIONS
+
 Ask the user for clarification if repository path or configuration file is ambiguous.
 
+## Code Review Behavior
+
+- When the same issue appears identically across multiple files, comment ONCE on the first occurrence and note how many other files are affected (e.g., "This same issue appears in 12 other sample files"). Do not post duplicate comments.
+- Do NOT comment on `pnpm-lock.yaml` — it is auto-generated by pnpm and not human-editable. Version mismatches are caught by CI.
+- PRs with titles starting with `[AutoPR` are auto-generated by SDK generation tooling. Focus review on public API surface issues (types, exports, naming). Do not comment on infrastructure files (`eslint.config.mjs`, `warp.config.yml`, `tsconfig.json`, `vitest.config.ts`) — their patterns are set by the generation tool.
+
 ## SDK release
 
-For detailed workflow instructions, see [SDK Release](https://github.com/Azure/azure-sdk-for-js/blob/main/eng/common/instructions/copilot/sdk-release.instructions.md).
+For detailed workflow instructions, invoke the `azsdk-common-sdk-release` skill.

.github/instructions/reviewer/lockfile.instructions.md

@@ -0,0 +1,10 @@
+---
+applyTo: "pnpm-lock.yaml"
+description: "Exclude pnpm lockfile from code review comments — it is auto-generated and not human-editable."
+---
+# Lockfile Review Rules
+
+- Do NOT comment on pnpm-lock.yaml changes
+- The lockfile is auto-generated by pnpm and is not human-editable
+- Specifier mismatches, version differences, or formatting changes are expected and validated by CI checks
+- No code review comments on this file are actionable

.github/instructions/reviewer/mgmt-sdk.instructions.md

@@ -63,9 +63,18 @@ Flag patterns indicating spec problems:
 
 ## Samples & Tests
 - Samples are auto-generated — only comment on syntax issues found while checking `src/` references
+- Do NOT comment on placeholder values in samples (e.g., `subscriptionId`, `resourceGroupName`) — these are intentionally non-real values
 - Do NOT comment on style, formatting, documentation, or whitespace
 - Do NOT comment on implementation internals (private methods, internal helpers)
 
+## Generated Infrastructure Files
+- Do NOT comment on `eslint.config.mjs`, `warp.config.yml`, `tsconfig.json`, or `vitest.config.ts` patterns — these are set by the generation tool and intentionally differ from hand-written packages
+- Config deviations from other packages are expected when generation tooling evolves
+
+## Comment Deduplication
+- If an issue repeats across multiple files (e.g., same placeholder format in every sample), comment ONCE on the first file and note the total count of affected files
+- Do NOT post the same comment on every file that has the same issue
+
 ## Issue Types
 **🔴 Tool Issue:** Generation bug → fix + report to [autorest.typescript](https://github.com/Azure/autorest.typescript/issues)
 **🔴 Design Issue:** API problem → `@clientName`/`@override` in spec repo