Fix Zod v4 deprecation warnings

[GrzywN]

This PR fixes 4 deprecation hints from zod package, hints are displayed since we updated Astro and other packages.

agentic-engineering on  @grzywn/cli-tips-for-agents [$+?] via 🥟 v1.3.11
❯ bun run lint
$ prettier --write . && astro check && bun links
.agents/skills/redactor/agents/openai.yaml 7ms (unchanged)
.github/workflows/ci.yml 2ms (unchanged)
.github/workflows/deploy.yml 2ms (unchanged)
.prettierrc.json 4ms (unchanged)
.vscode/extensions.json 1ms (unchanged)
astro.config.ts 18ms (unchanged)
package.json 1ms (unchanged)
scripts/links.ts 18ms (unchanged)
src/components/ExternalLink.astro 43ms (unchanged)
src/components/Footer.astro 9ms (unchanged)
src/components/Head.astro 4ms (unchanged)
src/components/JsonLD.astro 6ms (unchanged)
src/components/SkipLink.astro 6ms (unchanged)
src/components/TableOfContents.astro 6ms (unchanged)
src/content.config.ts 2ms (unchanged)
src/lib/links.ts 5ms (unchanged)
src/lib/siteLinks.ts 1ms (unchanged)
tsconfig.json 0ms (unchanged)
12:08:41 [content] Syncing content
12:08:41 [content] Synced content
12:08:41 [types] Generated 211ms
12:08:41 [check] Getting diagnostics for Astro files in /Users/user/p/agentic-engineering...
src/content.config.ts:13:4 - warning ts(6385): '(): ZodObject<{ "@type": ZodString; }, $loose>' is deprecated.

13   .passthrough();
      ~~~~~~~~~~~

src/lib/links.ts:18:23 - warning ts(6385): '(params?: string | { abort?: boolean | undefined; error?: string | $ZodErrorMap<$ZodIssueInvalidStringFormat> | undefined; message?: string | undefined; } | undefined): ZodString' is deprecated.

18   urldate: z.string().date(),
                         ~~~~
src/lib/links.ts:17:20 - warning ts(6385): '(params?: string | { abort?: boolean | undefined; error?: string | $ZodErrorMap<$ZodIssueInvalidStringFormat> | undefined; message?: string | undefined; } | undefined): ZodString' is deprecated.

17   date: z.string().date().or(z.literal("")),
                      ~~~~
src/lib/links.ts:14:19 - warning ts(6385): '(params?: string | { abort?: boolean | undefined; pattern?: RegExp | undefined; normalize?: boolean | undefined; protocol?: RegExp | undefined; hostname?: RegExp | undefined; error?: string | ... 1 more ... | undefined; message?: string | undefined; } | undefined): ZodString' is deprecated.

14   url: z.string().url(),
                     ~~~

Result (12 files):
- 0 errors
- 0 warnings
- 4 hints