Fix typos and formatting in documentation

[madisoncarter1234]

Fixed multiple documentation issues:

Typos:

1. casts.md: "th example" → "the example"
2. siwf/index.md: "Farcaste" → "Farcaster"
3. warpcast/api.md: "depracated" → "deprecated"
4. messages.md: "channels emoji" → "channels, and emoji"

Formatting:
5. verify-address.md: Added missing space after comma in link list

Link Consistency:
6. developers/index.md: Removed .md extensions from internal links for consistency

All simple text corrections to improve documentation quality.

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PR-Codex overview

This PR focuses on correcting typos and improving clarity in documentation related to the Farcaster platform.

Detailed summary

• Updated the demo description in docs/developers/siwf/index.md from "Farcaste" to "Farcaster".
• Added a comma in docs/developers/guides/writing/messages.md for clarity.
• Corrected "depracated" to "deprecated" in docs/reference/warpcast/api.md.
• Fixed spacing in a bullet point in docs/developers/guides/writing/verify-address.md.
• Adjusted links in docs/developers/index.md to remove file extensions.
• Corrected "th example" to "the example" in docs/developers/guides/writing/casts.md.

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