fix: prompt user for Terraform state bucket name to avoid S3 naming issue

[cstirry]

Problem

When a new deployer runs uv run opencontext authenticate, all checks pass cleanly — Python, uv, AWS CLI, credentials, and Terraform. But then when they run uv run opencontext configure and complete the CLI wizard, it fails at the end with no useful explanation:

Error: An error occurred (403) when calling the HeadBucket operation: Forbidden

The root cause is that the S3 bucket name for Terraform state was hardcoded to opencontext-terraform-state. S3 bucket names are globally/regionally? unique across all AWS accounts — this name is already owned by another account, so any new deployer hits a 403 with no actionable error message.

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How to reproduce the original bug

1. Clone the repo fresh
2. Run uv run opencontext authenticate — all checks pass
3. Run uv run opencontext configure and complete the wizard
4. At the end, after answering all questions, the process fails with:

Error: An error occurred (403) when calling the HeadBucket operation: Forbidden

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What's fixed

1. Interactive bucket name prompt with immediate validation

Instead of silently using a hardcoded bucket name, the wizard now prompts the user during the AWS Settings step. The default suggestion is opencontext-terraform-state but the user can change it. The bucket is validated immediately — if it's owned by another account, the user is told right away and re-prompted before continuing.

2. Always run terraform init -reconfigure

The original code skipped terraform init if a .terraform directory already existed. This caused a failure on re-runs when the bucket name changed — Terraform detected a backend config change and refused to proceed. Replacing the existence check with -reconfigure ensures the backend config is always in sync.

3. New _check_state_bucket() helper

Extracted bucket validation into a clean helper that returns "ok", "missing", or "taken" without crashing Rich's markup renderer with raw AWS error text.

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What it looks like now

AWS Settings
? AWS region: us-east-1
? Terraform state bucket name: opencontext-terraform-state
Bucket opencontext-terraform-state is owned by another AWS account. Please choose a different name.
? Terraform state bucket name: opencontext-terraform-state-govex

...

Terraform state bucket opencontext-terraform-state-govex not found. Creating...
Created S3 bucket opencontext-terraform-state-govex (region: us-east-1, versioning: enabled, encryption: AES256).

Configuration complete!
Next step: opencontext deploy --env staging

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Files changed

• cli/commands/configure.py — all logic changes
• tests/test_cli_configure.py — updated wizard responses and assertions
• tests/test_cli_configure_extended.py — added boto3.client mock and bucket prompt response to all wizard tests

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Note on Terraform files

terraform/bootstrap/variables.tf and terraform/aws/main.tf still contain
the hardcoded default opencontext-terraform-state. These are not changed in
this PR because configure.py passes the bucket name to Terraform at init time
via -backend-config=bucket=<name>, which overrides the hardcoded default at
runtime.

However, anyone running terraform init directly (bypassing the CLI) would
still hit the same naming collision. May want to consider updating those files
to remove the hardcoded default if that could be an issue.

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Screenshot Before

Screenshot After

[cstirry]

Need to update whatever README is relevant for this