docs(swidge): add BOB Gateway swidge module

[nud3l]

Adds documentation for @gobob/wdk-protocol-swidge-gateway, a community swidge provider for native BTC routes.

BTC is spent and received on Bitcoin L1 — no wrapped-BTC intermediary, no custodian, and keys never leave the WDK account. The module implements the full SwidgeProtocol interface and registers through WDK core like any other provider.

What it covers

Route	Support
BTC → tokens on Ethereum, Base, Arbitrum, BSC (USDT, USDC, ETH, wBTC, cbBTC, XAUT)	Supported
Tokens on EVM → native BTC	Supported (approval required)
BTC → USDT on Tron	Destination only
EVM ↔ EVM	Inherited swap() / bridge()

Pages added

Under /sdk/swidge-modules/swidge-gateway/, mirroring the structure of the existing Rhino.fi module:

• index — overview, supported routes, execution model
• configuration — source chain, slippage, affiliate fees, BTC fee rate, API access, ERC-4337 paymaster
• usage — install, register, discover, quote, onramp, offramp, EVM↔EVM, status, errors
• api-reference — constructor, methods, route options, status mapping, error codes

Listed in all-modules, swidge-modules, and community-modules, and added to the sidebar in custom-tree.ts.

Two things integrators need, called out explicitly in the docs: the gateway broadcasts the Bitcoin transaction on onramp routes (the module does not), and the Gateway API applies a country blocklist (including the US and UK) that returns 403 — which affects CI as well as production.

Verified against the published package

Every code sample in the usage guide follows the registerProtocol wiring, which we confirmed end-to-end against mainnet using the published 0.2.0 from npm:

getSwidgeProtocol("gateway") -> GatewaySwidge
LIVE QUOTE (0.001 BTC -> USDT@ethereum)
  toTokenAmount: 63884707 (USDT, 6dp) = 63.884707

Note on the "Released provider modules" table

The table in swidge-modules/index.mdx was missing Rhino.fi (it lists only Orchestra, though Rhino.fi is documented and appears in all-modules). I added that row alongside ours — happy to drop it if you'd rather keep this PR to a single module.

Verification

• npm run check:meta — pass
• npm run check:links — pass (264 files, 1420 internal links, 739 anchors, 0 broken)

npm run build could not be run locally: it requires @tetherto/docs-seo-schema from GitHub Packages, which returns 401 without Tether org authentication. The new pages resolve as routes under the link checker and the nav entry mirrors the adjacent Rhino.fi folder exactly, but the Next.js build and OG generation are unverified on our side and will need CI.