Add Wraith name subscriptions tutorial

[kelvin1738-sys]

Overview

Adds a new Stellar guide for building recurring subscriptions around .wraith names instead of raw stealth meta-addresses.

Related Issue

Closes #127

Changes

• Added guides/stellar/subscriptions-with-wraith-names.mdx.
• Documented the off-chain scheduler pattern that resolves merchant.wraith on every billing run.
• Added a Futurenet fixture-backed example for the subscription flow while live Wraith Futurenet contracts are unavailable.
• Covered mid-subscription name rotation, payer-side cancellation, missed-payment handling, and name-expiry behavior.
• Cross-linked the guide with the Wraith names lifecycle guide, Stellar payment links guide, and Spectre + Stellar Cookbook Recipe 2.
• Added the new page to the Guides navigation in docs.json.

Verification Results

• corepack.cmd pnpm install --frozen-lockfile completed dependency installation after approving local build scripts with corepack.cmd pnpm approve-builds --all.
• corepack.cmd pnpm run check:nav-coverage passed: 70 pages checked, 70 nav entries verified.
• Equivalent snippet compilation passed by running the repo checker with its child TypeScript invocation pointed directly at node_modules/typescript/bin/tsc: 70 MDX files scanned, 630 code fences found, 616 checked snippets, 14 skipped no-check snippets.
• git diff --check passed.
• corepack.cmd pnpm test could not complete on this Windows shell because scripts/check-snippets.ts spawns pnpm with shell: false, and this environment exposes pnpm through corepack.cmd rather than a pnpm executable (spawn pnpm ENOENT).
• corepack.cmd pnpm exec mint validate could not complete locally because pnpm regenerated local build-script approval metadata after the temporary approval file was intentionally removed from the worktree.

Acceptance Criteria

Criteria	Status
Example runs against futurenet fixtures	Done
Renders in mint dev	Not run locally; Mint CLI was unavailable in this shell
Passes Compile docs snippets CI	Snippet compilation passed with equivalent direct TypeScript invocation
Cross-linked with required pages	Done
Nav entry under Guides	Done

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[truthixify]

Merged @kelvin1738-sys. You hit the angle the issue was actually about: keying the subscription to the .wraith name rather than a raw meta-address, so the recipient can rotate without breaking the payer's schedule. Rotation and name-expiry get real coverage (15 and 16 mentions respectively) instead of a passing note, and you cross-linked the cookbook payroll recipe and the payment-links page rather than restating their mechanics. That was the whole point of the rewrite I did on the issue, so thanks for reading it.