docs: add solana bridge to main bridges page, reorganize content, update metadata description

[roethke]

What changed? Why?
Updates the main bridge anchor page to serve as a unified landing page covering all supported bridging options.

• Reorganized content by source chain
• Added Base-Solana bridge section with key features, contract addresses table, and links to full documentation
• Added "For Token Issuers" section linking to the L1 token bridging guide
• Added new FAQ entry explaining Base-Solana bridge works
• Updated front-matter metadata description

Notes to reviewers

How has it been tested?
Locally

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1