Fixes #14116

Before wrangler on every command would trigger the skills installation flow when it checks for agents configurations and after an interactive prompt potentially installs them for the user (at most once).

This had many various edge cases and downsides, like:

• disturbing/surprising users with this interactive prompt unrelated to their current task
• interrupting the user's flow
• not working well for parallel wrangler executions (where they could each hid the prompt of the other, effectively blocking them)

Now instead the question is presented after the successful execution of non-long lived commands (such as wrangler login), this doesn't insert the prompt upfront for every command so it should address all the problematic edge case scenarios we've seen.

Additionally this PR adds extra logic to save the skills metadata file before asking the prompt (and potentially overriding it after), this should ensure that user should not see this prompt more than once.

Example of new flow:

$ npx https://pkg.pr.new/wrangler@14264 whoami 

 ⛅️ wrangler 4.100.0 (dario/install-skills-scoped)
──────────────────────────────────────────────────
Getting User settings...
👋 You are logged in with an OAuth Token, associated with the email dario@cloudflare.com.
┌──────────────┬──────────────────────────────────┐
│ Account Name │ Account ID                       │
├──────────────┼──────────────────────────────────┤
│ ...          │ ...                              │
└──────────────┴──────────────────────────────────┘
🔓 Token Permissions:
Scope (Access)
- ...

? Before you go, Wrangler detected potential configurations for the following AI coding agents on your system likely without Cloudflare skills: Claude Code, OpenCode, GitHub Copilot. Would you like Wrangler to automatically install the Cloudflare skills for you? › (Y/n)

To try the flow just run one of the Wrangler commands that trigger this using the prerelease, like for example:

$ npx https://pkg.pr.new/wrangler@14264 whoami 

(To trigger this make sure not to have a agents-skills-install.jsonc file in your global .wrangler directory)

• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
  • Additional testing not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: self explanatory feature / behavior

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