fix(@angular/cli): fallback to local package.json for schematic detection on first run

[clydin]

Private package registries frequently strip out custom non-npm metadata properties such as "schematics" or "ng-add" from their remote API responses. This causes ng add to bypass executing schematics on the first run.

This fix adds a fallback check immediately after package installation: if the registry did not report hasSchematics as true, the CLI falls back to resolving and reading the physically installed package's package.json on disk as the single source of truth.

Additionally, if the local manifest specifies ng-add.save: false (but it was persistently installed due to registry omissions), it programmatically prunes the package from dependencies or devDependencies post-execution, and executes a silent packageManager.install() to cleanly remove the physical package files and update the lockfile.

Fixes #33060

[gemini-code-assist]

Code Review

This pull request adds support for detecting and cleaning up temporary dependencies during ng add when the package's package.json specifies ng-add.save = false, even if the registry metadata is stripped. It also includes an E2E test to verify this behavior. The reviewer suggested wrapping the cleanup logic in a try...catch block to ensure that any cleanup failure does not fail the entire command, and appending a trailing newline when writing back package.json to prevent formatting issues.

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