feat: add Lost & Found Exchange project

[MEHWISH310]

Description

Adds a new static project — Lost & Found Exchange — under projects/lost-and-found-platform/. It lets users report lost or found items, browse reports with nearby/keyword-based match suggestions, verify claims via QR codes (generate + scan), and message the other party through a per-report chat thread. Built as a single-file HTML/CSS/JS app (no backend, localStorage for persistence), following the same design system and CDN libraries (qrcode-generator, jsQR) used in qr-code-toolkit.

Fixes #93

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings or errors.
• I have tested my code locally by running the project.

Screenshot

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