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 adds a complete 8-step Flutter tutorial for building an ideas-tracker app with Appwrite, replacing the previous "coming soon" placeholder. Previously flagged concerns (missing obscureText, fire-and-forget async calls, missing mounted checks, missing database creation step, and debugPrint inconsistency) have all been resolved in this revision.

Confidence Score: 5/5

• Safe to merge; all prior P1 concerns are resolved and only minor P2 suggestions remain.
• All previously flagged issues (async/await, mounted checks, obscureText, debugPrint consistency, database/collection ID guidance) are addressed. The two remaining findings are quality-of-life improvements for tutorial clarity, not correctness issues.
• No files require special attention.

Important Files Changed

Filename	Overview
src/routes/docs/tutorials/flutter/step-4/+page.markdoc	Authentication step with UserProvider; previously flagged issues (obscureText, async/await, mounted checks) are all resolved.
src/routes/docs/tutorials/flutter/step-5/+page.markdoc	Routing step; the Routes widget has no loading state, so returning authenticated users briefly see a flash of the Login screen during auth init.
src/routes/docs/tutorials/flutter/step-6/+page.markdoc	Database step; previously flagged issues resolved. Minor: inline comment on ideasDatabaseId says "Replace with your database ID" but the tutorial explicitly tells users to use "default", which is already in the code.
src/routes/docs/tutorials/flutter/step-7/+page.markdoc	Ideas page with submit/remove; previously flagged async/mounted issues are correctly addressed in this version.

_{Reviews (12): Last reviewed commit: "specify to replace <REGION> in appwrite ..." | Re-trigger Greptile}

[greptile-apps]

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