docs(github) : Add githubissue templates for bugs, features, and docs

[ayushsri-dev]

Summary

This PR adds standardized, classic Markdown issue templates under .github/ISSUE_TEMPLATE/ to streamline issue reporting, feature proposals, UI/UX feedback, and documentation fixes across the Arvio repository.

By using classic .md templates instead of structured forms, contributors can report issues directly inside GitHub's standard Markdown editor with pre-populated headings, code fences, and helpful guidance comments.

Changes Introduced

Added .github/ISSUE_TEMPLATE/:

• bug_report.md: Pre-filled Markdown template for reproducible bug reports across Arvio platforms (Android TV/Mobile, Web, iOS, Supabase, Resolver Worker, IPTV, Player Engine). Includes version/device placeholders, a shell code block for logs, screenshot sections, and Content & Source Policy verification.

• feature_request.md: Structured template for functional enhancements, integrations, and subsystem improvements.

• documentation.md: Template for reporting documentation errors or proposing updates to READMEs and setup guides.

• config.yml: Configures template intake with blank_issues_enabled: true and includes links to repository documentation and policy guidelines.

Benefits

• Better Contributor Experience: Opens GitHub's standard single-field Markdown editor with pre-populated structures and non-rendering <!-- HTML guidance comments -->.
• Faster Triage: Prompts contributors to specify their environment, device class (Android TV D-pad vs. Mobile Touch vs. Web), build variant (play vs sideload), and diagnostic logs upfront.
• Policy Enforcement: Includes pre-submission checkboxes to ensure issue reports adhere to Arvio's Content & Source Policy.

Verification

• Verified YAML frontmatter validity (name, about, title, labels, assignees).
• Verified Markdown code fences and HTML comment syntax.
• Verified .github/ISSUE_TEMPLATE/ directory structure and config.yml settings.

Closes #484