Create strings.xml for Chinese localization

[ALILEX-1]

Add Chinese (Simplified) localization for app strings.

[jeiel85]

Thank you — this is a genuinely careful piece of work, and it holds up to the checks I can actually run:

• 317 strings and 9 plurals, exact key parity with values/strings.xml. Nothing missing, nothing extra.
• Every format specifier matches — all positional (%1$s, %1$d, %2$d, %3$d) arguments line up with the source on all 21 formatted strings.
• \n escapes preserved on every multi-line string.
• The right things were left untranslated — app name, URLs, Apache License 2.0, Material You, tag_result_format. That is exactly the set the other five locales leave alone, and getting it wrong in either direction is the usual way a translation PR breaks something.
• You carried over the explanatory comments from the source file (the archive noun-vs-verb note, the elapsed_* note). That is the tell that you read the file rather than fed it through a machine.

Rather than send you back and forth over repo plumbing you have no reason to know about, I pushed a follow-up commit to this branch. Three things, all of them our side of the fence:

1. Registered zh in the two translation gates. This repo checks translations with ResourceParityTest and UntranslatedStringTest, and both take a hard-coded locale list — so values-zh would have shipped without either of them ever looking at it. That is our design, not something a contributor should have to discover.
2. Dropped quantity="one" from the 9 plurals. Chinese has only other in CLDR, so that item can never be selected; values-ko and values-ja ship other only for the same reason.
3. Kept the directory as values-zh. Worth naming since it is a real fork in the road: values-zh is a language-level match, so Traditional locales (zh-Hant-TW, zh-Hant-HK) get your Simplified text rather than falling back to English. I decided that is the better default — a partially-understood UI beats an English one, and a zh-Hant locale can be added later without moving this file. If you meant it strictly as Simplified-only, say so and I will rename it.

Verified before pushing: both gate tests pass with zh registered, and :app:lintRelease is green. The one lint warning on your file is TypographyEllipsis on search_notes_hint — the English source and values-ja/ko/es/fr all carry the same one, so you matched the house style exactly.

One thing left, if you are willing

app/src/main/res/raw-<locale>/starter_notes.md holds the six sample notes a user sees on first launch. There is no raw-zh yet, so a Chinese device falls back to the English ones. That works, so it is not blocking this PR — but it is the first screen anyone sees, and it is 136 lines of actual prose rather than UI labels. I would rather not write it myself: I can diff a file and count keys, but I cannot tell whether the sentences sound like something a person would write, which is the entire value of what you contributed here.

If you would like to take it, a separate PR is perfect. If not, that is completely fine — say so and I will find another way.

The public side of Chinese support — landing page, privacy policy, README — is in #295, waiting on this one. You are credited in THANKS.md there.