Fixes #724

## Description
Setting `"notices": false` in cdk.json doesn't suppress notices.

The root cause is that we handle logic to determine whether we should
print notices at *yargs*. Yargs had a default value determined by a
helper function (`YARGS_HELPERS.shouldDisplayNotices()`) that returned
true when not in CI, or when in a safe CI.

This meant that any setting in our configuration would be overwritten by
the output of this helper, because it looks like it's coming from the
command line!

## Solution

Centralize logic for notices in `cli.ts`.

Made the notices option in yargs `undefined` by default. Moved the logic
from `YARGS_HELPERS.shouldDisplayNotices()` into the `cli.ts`. This has
several implications.
- Setting `notices` in config now functions as expected; it will still
not override the command line setting
- If a CDK app is running in a CI environment where it would not be safe
to print notices
- NEW BEHAVIOR: Notices WILL be printed if `notices: true` or `notices:
[truthy value]` is set in config
- Notices WILL be printed if flag `--notices` is passed, and NOT printed
if `--no-notices` / `--notices=false` is passed at the command line (was
already the case)

**Caveat: `"notices": "false"` in the config will suppress notices, but
other "truthy" values will cause them to be printed.**

### Testing
Added unit tests to verify the hierarchy of behavior:
1. Flags in CLI (`--notices` or `--no-notices`)
2. Setting in configuration (`"notices": false` in cdk.json)
3. Print notices if not in CI or in CI where it is safe

---
By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license

---------

Signed-off-by: github-actions <[email protected]>
Co-authored-by: github-actions <[email protected]>

Fixes #832 

Currently, running `cdk flags --set` or `cdk flags --set --recommended`
is a no-op. Either the `--all` or `--unconfigured` options should be
passed alongside `--set`. This can be attributed to insufficient testing
during development of the feature.

Changes:
- Added validation to fix the problem above
- Brought `flag-operations.ts` to 100% unit test line coverage
(previously 92%)

<img width="1498" height="137" alt="Screenshot 2025-09-03 at 12 41 21"
src="https://github.com/user-attachments/assets/1a9ad22d-4a78-411a-bb09-de4975d8752a"
/>

Validated with unit tests and manual testing.

---
By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license

---------

Signed-off-by: github-actions <[email protected]>
Co-authored-by: github-actions <[email protected]>

This change introduces the creation and execution of stack refactors. It
builds on previous work that put all the pieces in place (mapping
computation, mapping file reading, exclude lists, dry-run etc). The
following flowcharts summarize the behavior in interactive and
non-interactive modes, for each environment in the application:

#### Non-interactive case

```mermaid
flowchart LR
    mapping{Refactor file present?}
    empty{Empty mapping?}
    dryrun{--dry-run?}
    compute[Compute mapping]
    use[Use mapping]
    print[Print mapping]
    mapping ---|No| compute
    mapping ---|Yes| use
    compute --- empty
    use --- empty
    empty ---|Yes| Exit
    empty ---|No| print
    print --- dryrun
    dryrun ---|Yes| Exit
    dryrun ---|No| Refactor
    Refactor --- Exit
```

#### Interactive case

```mermaid
flowchart LR
    mapping{Refactor file present?}
    empty{Empty mapping?}
    dryrun{--dry-run?}
    force{--force?}
    compute[Compute mapping]
    use[Use mapping]
    print[Print mapping]
    ask[Ask user]
    mapping ---|No| compute
    mapping ---|Yes| use
    compute --- empty
    use --- empty
    empty ---|Yes| Exit
    empty ---|No| print
    print --- dryrun
    dryrun ---|Yes| Exit
    dryrun ---|No| force
    force ---|Yes| Refactor
    force ---|No| ask
    ask ---|Yes| Refactor
    ask ---|No| Exit
    Refactor --- Exit
```

Closes #140.

---
By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license