fix: restore monorepo dev server support

[VaibhavAcharya]

Summary

After PR #7366 (v22.1.7+), running netlify dev --cwd ./ from a monorepo package directory fails to start framework dev servers. This breaks local development workflows for monorepo users.

When --cwd ./ resolves to process.cwd(), That PR deletes the flags.cwd. This triggers logic in run-build.ts:110 that incorrectly switches to the workspace root even when running from a package subdirectory, preventing framework binaries from being found.

Add isRoot check to the workspace root logic in run-build.ts, matching the same condition used in base-command.ts:544.

Fixes #EX-552
Fixes #7392 #7528

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[github-actions]

📊 Benchmark results

Comparing with 0b24fc1

• Dependency count: 1,130 (no change)
• Package size: 321 MB (no change)
• Number of ts-expect-error directives: 380 (no change)

[VitaliyR]

Looks good to me but make sure to test it good - since monorepos has a lot of possible ways being used

[serhalp]

@VaibhavAcharya I think this addresses #7528 and #7392, does that sound right?

[aitchiss]

looks sensible, but +1 to Vitalii's comment about making sure we've thoroughly tested this one!