Update syncpack to v15 and move pnpm overrides to pnpm workspace file

[alexvy86]

Description

Update syncpack to v15 in the client release group so we can move pnpm overrides to pnpm-workspace.yaml file (also done here). Before that version, syncpack didn't fully support processing overrides in the workspace file.

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I confirmed that making changes to deps in catalogs: are flagged correctly per the syncpack configuration. Also of note, today syncpack config in the client release group already ignores everything in pnpm overrides. I confirmed that updating that config and doing something "bad" in those deps in their new location, gets flagged correctly.

[alexvy86]

Note for reviewers: this seems to have been a bug fixed in syncpack 15, not sure why it wasn't getting flagged before.

[github-actions]

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[Copilot]

Pull request overview

Updates the client release group’s dependency tooling by upgrading syncpack to v15 and relocating pnpm override configuration from package.json into pnpm-workspace.yaml, aligning with the newer pnpm workspace configuration model and keeping override rationale as YAML comments.

Changes:

• Bumped syncpack from ^14.0.2 to ^15.1.2 (and updated lockfile artifacts accordingly).
• Moved pnpm.overrides (and associated explanatory comments) out of root package.json into root pnpm-workspace.yaml.
• Adjusted docs and syncpack rules to reflect/allow current dependency pinning behavior.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pnpm-workspace.yaml	Adds workspace-level overrides: with in-file rationale comments.
pnpm-lock.yaml	Updates lockfile entries for syncpack@15.1.2 and override materialization.
package.json	Updates syncpack devDependency and removes pnpm.overrides/comment scaffolding.
build-tools/README.md	Updates local testing guidance to use pnpm-workspace.yaml overrides.
.syncpackrc.yml	Allows exact pinning for @tylerbu/markdown-magic in semver rules.

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported

[jason-ha]

:)
Note that #27307 also moves these and conflict will need resolved. But that is blocked per so I think this is good to proceed.