feat(project): scaffold add harness handler

[Hweinstock]

Problem

We're missing functionality to add resources to a project. This PR sets up the handler for agentcore project add harness as an example, and scaffolds the remaining work for add.

Solution

• setup a handler that takes the same flags at the imperative harness create (with a extra few project specific ones). Alternatively considered using different flags from imperative, but this creates an inconsistent UX where project command inputs are similar to api shapes, but slightly different (ex. containerUri is top level, vs nested in json).
• convert those flags into the spec format expected by the schemas.
• scaffold an add function for the shared functionality.

Testing / Verification

• created a project, attempted to add a harness and got the not implemented error.
• add unit tests for the flag parsing.

Next Steps

• I want to move the scaffolding of runtime into the add function, then call that from the handler when we're scaffolding. This will make it easier to re-use the logic, and handle harness in the same place.
• implement the rest of add via json source.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 99.50860% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.96%. Comparing base (9398c03) to head (d9138cd).
⚠️ Report is 1 commits behind head on refactor.

Files with missing lines	Patch %	Lines
src/handlers/project/add/harness/index.ts	99.48%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           refactor    #1998      +/-   ##
============================================
+ Coverage     96.91%   96.96%   +0.04%     
============================================
  Files           356      357       +1     
  Lines         20136    20531     +395     
============================================
+ Hits          19515    19908     +393     
- Misses          621      623       +2     

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[Hweinstock]

i'm imagining minimal special casing here. We'll want to scaffold files for runtime/harness, then the rest should be simple shared logic to write the schema changes. We will also need some special casing for harness since it links to the config in the scaffolded files.

[Hweinstock]

we handle all the api shape --> project schema conversion in the handler to keep the shared logic clean.