fix: validate unique API name before generating authoring bundle @W-21258874@

[marcelinollano]

What does this PR do?

Prevents overwriting existing local agent script bundles by checking if an authoring bundle with the same API name already exists on disk before generating a new one. When a duplicate is detected, the user is prompted to overwrite (yes), enter a new name (no), or cancel. A --force-overwrite flag is also added for non-interactive usage.

What issues does this PR fix or reference?

@W-21258874@

Functionality Before

Running sf agent generate authoring-bundle with an API name that already exists locally would silently overwrite the existing bundle files without warning.

Functionality After

• If the target aiAuthoringBundles/<api-name>/ directory already exists, the user is prompted: "An authoring bundle with the API name X already exists. Overwrite it? (y/N/cancel)"
• Yes: proceeds with overwrite
• No: restarts the flow, re-prompting for both bundle name and API name
• Cancel: exits gracefully
• --force-overwrite flag skips the check entirely

Testing Setup Notes

1. Create an authoring bundle: sf agent generate authoring-bundle --no-spec --name "Test Agent" --api-name TestAgent --target-org <org>
2. Run the same command again with the same API name to trigger the duplicate detection prompt
3. Verify all three prompt responses (yes/no/cancel) behave as expected
4. Verify --force-overwrite bypasses the prompt

[WillieRuemmele]

QA Notes

---

✅ : given y/n/cancel prompt when AAB exists

 ➜  ../../oss/plugin-agent/bin/run.js agent generate authoring-bundle
✔ Select an authoring bundle template Default template (Recommended)
✔ Enter the authoring bundle name ForQA
✔ Enter authoring bundle API name ForQA
✔ An authoring bundle with the API name "ForQA" already exists. Overwrite it? No
✔ Enter the authoring bundle name ForQA1
✔ Enter authoring bundle API name ForQA1
Generating authoring bundle: ForQA1... done
Authoring bundle "ForQA1" was generated successfully.

✅ : cancel -> cancels command