add flutter tutorial to build an ideas tracker app using appwrite

[blueberry-adii]

What does this PR do?

This PR introduces flutter tutorial to create an ideas tracker app using appwrite in the Appwrite Docs

Test Plan

Build tests for Android and iOS runs and works well using flutter run

Related Issues

This PR closes #2882

Have you read the Contributing Guidelines on issues?

Yes.

[greptile-apps]

Greptile Summary

This PR replaces the Flutter tutorial placeholder with a complete 8-step guide for building an ideas tracker app using Appwrite and the Provider pattern. All previously identified concerns (password plaintext, fire-and-forget async calls, missing !mounted guards, missing database creation step, undocumented Varchar sizes, and inconsistent debugPrint usage) have been addressed in this revision. The two remaining findings are minor documentation inconsistencies in step-1 and step-6 that have no impact on the tutorial's correctness.

Confidence Score: 5/5

• This PR is safe to merge — all previously flagged P0/P1 issues are resolved and only minor P2 documentation nits remain.
• All nine previously raised concerns (security, async error handling, mounted guards, database setup completeness, etc.) have been addressed. The two new findings are P2 text inconsistencies with no runtime impact.
• No files require special attention.

Important Files Changed

Filename	Overview
src/routes/docs/tutorials/flutter/step-4/+page.markdoc	New authentication step with UserProvider and Login widget. All previously flagged issues resolved: obscureText: true present, async calls awaited, try/catch with error SnackBar, and !mounted guards in place.
src/routes/docs/tutorials/flutter/step-6/+page.markdoc	New database step with IdeasProvider. Previously flagged issues resolved (create DB section added, Varchar sizes included, collection ID specified, debugPrint used consistently). Minor narrative inaccuracy at line 127: refers to idea.userId which doesn't match the code.
src/routes/docs/tutorials/flutter/step-7/+page.markdoc	New ideas page with form submission and removal. All previously flagged issues resolved: both add() and remove() are awaited with try/catch, !mounted guards in place, and controllers only cleared on success.

_{Reviews (10): Last reviewed commit: "replace Styles.disabledButton by adding ..." | Re-trigger Greptile}