fix(upgrade): detect npm install method from node_modules path (#723)

## Summary

- Add `detectPackageManagerFromPath()` — a fast path-based check that
detects npm/pnpm installation by examining `process.argv[1]` for a
`node_modules` segment
- Wire it into the detection cascade after Homebrew (`/Cellar/`) and
before the DB lookup, mirroring the same authoritative-override pattern
- Persists the detected method to SQLite so subsequent runs skip even
this cheap check

## Problem

When the CLI is installed via npm and run on Windows (especially via
NVM/Laravel Herd), spawning `npm`, `pnpm`, `bun`, `yarn` to detect the
install method fails with ENOENT because `.cmd` files aren't found by
`spawn()` without `shell: true`. This left the method as `"unknown"`,
blocking `sentry cli upgrade` entirely — even though the CLI was clearly
running from a `node_modules` directory.

## Approach

Rather than fixing the Windows spawn issue (which would still be slow
and fragile), add a fast path check that examines the script path for a
`node_modules` segment — the same pattern used by the Homebrew
`/Cellar/` check. Cross-platform (splits on both `/` and `\`), handles
Windows 8.3 short paths, and distinguishes pnpm via its `.pnpm`
directory.

Fixes CLI-Y1

Author: BYK