feat: add `asc builds next-number` command

[hanrw]

Summary

Add a builds next-number command that returns the next available build number for a given app/version/platform combination. This eliminates manual lookup when uploading builds.

Motivation

After uploading builds, the build number must be unique per version/platform. Currently users must:

1. Run asc builds list --app-id <id> --version <ver> --platform <plat>
2. Manually find the highest build number from JSON output
3. Increment it

This is error-prone and not automation-friendly.

Proposed Command

asc builds next-number --app-id <id> --version <version> --platform <platform>

All three flags are required — you need to know exactly which version/platform you're targeting.

Use Cases

CI/CD Pipeline Automation

NEXT_BUILD=$(asc builds next-number --app-id $APP_ID --version 1.0.1 --platform ios)
asc builds archive --scheme MyApp --upload \
  --app-id $APP_ID --version 1.0.1 --build-number $NEXT_BUILD

Local Dev Before Upload

asc builds next-number --app-id 6748760927 --version 1.0.1 --platform ios
# → 4

Multi-Platform Apps

asc builds next-number --app-id $ID --version 2.0 --platform ios     # → 12
asc builds next-number --app-id $ID --version 2.0 --platform macos   # → 5

Expected Behavior

• Queries existing builds via listBuilds(appId:platform:version:)
• Finds max buildNumber (parsed as integer)
• Returns max + 1
• If no builds exist for the version, returns 1
• Default output: plain number (for scripting)
• --output json output includes affordance: "uploadBuild": "asc builds upload --app-id ... --version ... --build-number <next>"

Example Output

Given builds with numbers 1, 2, 3 for version 1.0.1/iOS:

$ asc builds next-number --app-id 6748760927 --version 1.0.1 --platform ios
4

$ asc builds next-number --app-id 6748760927 --version 1.0.1 --platform ios --output json --pretty
{
  "data" : {
    "affordances" : {
      "uploadBuild" : "asc builds upload --app-id 6748760927 --file <path> --version 1.0.1 --build-number 4 --platform ios"
    },
    "appId" : "6748760927",
    "nextBuildNumber" : 4,
    "platform" : "IOS",
    "version" : "1.0.1"
  }
}

Edge Cases

• Non-numeric build numbers: warn and skip when computing max
• No existing builds: return 1
• All builds expired or failed: still count them (build numbers are consumed regardless)

[hanrw]

Implemented in this session:

• asc builds list --platform --version — filter builds by platform and marketing version
• asc builds next-number --app-id --version --platform — auto-resolve next build number
• Build model now includes buildNumber (from Build.attributes.version) and platform (from included PreReleaseVersion)
• All release/upload/archive skills updated to use next-number instead of hardcoded build numbers
• GitHub Actions workflow templates updated with archive-from-source option