docs: wrap fence-syntax demos in 4-backtick md outer fences

Markdown renderers strip the fence info string when rendering a code
block, so a literal \`\`\`ts test name=\"...\"\`\`\` block in the source
showed up to readers as a plain ts code block — the marker that the
example was teaching was invisible.

Wrap every fence-syntax demonstration in a 4-backtick md outer fence
so the inner triple-backtick fence (with its info string intact) is
displayed verbatim. Affects:

* README.md - the 'Write a doctest' example
* docs/writing-tests.md - the intro example, the auto-injected
  helpers example, and the imports example
* docs/options.md - the name=, skip, only, and combined examples

The Imports section in writing-tests.md and the Combining options
section in options.md were already wrapped — converted them from the
md title="example" form to the plain md form for consistency.

Author: roll

README.md

@@ -18,10 +18,12 @@ Add `test` to any TypeScript fence in any `.md` file. The block's body becomes
 the body of an `it()` named after the nearest preceding heading. `describe`,
 `it`, and `expect` are injected for you.
 
+````md
 ```ts test
 import { sum } from "./sum.ts"
 expect(sum(1, 2)).toBe(3)
 ```
+````
 
 Untagged `ts` blocks render normally and are not run, so you can mix
 illustrative snippets and runnable assertions in the same article.

docs/options.md

@@ -24,9 +24,11 @@ parametric options, bare tokens for booleans.
 Useful when the heading is too generic or you want stable names regardless of
 heading edits.
 
+````md
 ```ts test name="adds two positive numbers"
 expect(1 + 1).toBe(2)
 ```
+````
 
 User-supplied names are passed through verbatim — no `#1`/`#2` suffixing even
 on collisions.
@@ -36,27 +38,31 @@ on collisions.
 Marks the block so vitest/jest reports it but doesn't execute it. Useful for
 documenting behavior that's pending or temporarily broken.
 
+````md
 ```ts test skip
 // not executed
 ```
+````
 
 ## Focusing on one test
 
 Mirrors vitest/jest `it.only(...)` — only this block runs in its file; all
 others are skipped.
 
+````md
 ```ts test only
 expect(true).toBe(true)
 ```
+````
 
 ## Combining options
 
 Options can be combined freely. When both `skip` and `only` are set on the
 same block, `skip` wins (safer default for CI: no-op the marker rather than
 silently focus).
 
-```md title="example"
-\`\`\`ts test only name="focus me"
+````md
+```ts test only name="focus me"
 expect(true).toBe(true)
-\`\`\`
 ```
+````

docs/writing-tests.md

@@ -11,13 +11,14 @@ description: Mark code blocks as runnable tests and how testdocs picks them up.
 Mark a code block in any `.md` file as a runnable test by adding `test` to its
 fence info string:
 
+````md
 ```ts test
 expect(1 + 1).toBe(2)
 ```
+````
 
-The fence above is a real test. Untagged `ts` blocks render normally and are
-not run, so you can freely mix illustrative snippets and runnable assertions
-in the same article.
+Untagged `ts` blocks render normally and are not run, so you can freely mix
+illustrative snippets and runnable assertions in the same article.
 
 ## Test names
 
@@ -31,24 +32,26 @@ see [Per-block options](/options/).
 `describe`, `it`, and `expect` are injected at the top of the generated test
 module — you don't need to import them. Doctest bodies stay clean:
 
+````md
 ```ts test
 const items = [1, 2, 3]
 expect(items.length).toBe(3)
 ```
+````
 
 ## Imports
 
 Any `import` statements inside a runnable block are hoisted to the module top
 and shared across every test in the same `.md` file. Multi-line imports work
 because the parser uses a real TypeScript AST (ts-morph), not a regex.
 
-```md title="example"
-\`\`\`ts test
+````md
+```ts test
 import { sum } from "./sum.ts"
 
 expect(sum(1, 2)).toBe(3)
-\`\`\`
 ```
+````
 
 ## Supported languages