Add community text submissions, and make custom text usable for study

Submissions
- POST /api/texts proposes a passage; nothing reaches players until a
  moderator approves it. GET /api/texts serves the approved set, which the
  client merges on top of its bundled packs at startup.
- Validation the server enforces rather than trusts: category from a fixed
  list, 40 to 600 characters, no control characters (a newline makes a
  passage untypeable in a single-line input), attribution length, and a
  unique index on md5(lower(btrim(content))) so the same passage cannot be
  submitted twice under different whitespace or casing.
- Moderation is a flag on users. The queue and the review endpoint both
  refuse a non-moderator, and reviewing an already-reviewed submission is a
  404 rather than a silent second write.
- Submissions are rate limited per user: enough for a real contributor, not
  enough to fill the queue from a script.
- A Contribute screen carries the form, your own submissions with their
  status, and - for moderators only - the review queue.

This is the half of TypeRacer's model the packs could not reach by authoring:
their corpus is roughly twelve thousand passages, grown by submission.

Custom text as a study tool
- Imported documents are kept between visits, with how far through each one
  you are. Custom text lived only in memory, so importing a set of notes and
  reloading the page lost them - fine for pasting a paragraph to race,
  useless for working through a file over several sittings.
- Position is recorded when a segment is finished, not when the next is
  started, so closing the tab after a segment does not lose it.
- Markdown is chunked as markdown: fenced code blocks are kept whole and
  typed line by line, and the decoration - hashes, asterisks, backticks,
  link brackets, table pipes - is stripped so what you retype is the
  material rather than the punctuation around it.
- Everything stays on the device. Notes are not uploaded anywhere.

Fixed while doing it: a chunk could contain a newline, which cannot be typed
in a single-line input at all. Any paragraph with a line break inside it --
ordinary in notes and in wrapped prose - produced an unfinishable segment.
Whitespace inside a chunk is now flattened.

1 files changed, 129 insertions, 0 deletions

diff --git a/web/src/styles.css b/web/src/styles.css
index 6a04db2..bb92393 100644
--- a/web/src/styles.css
+++ b/web/src/styles.css
@@ -2920,3 +2920,132 @@ body::-webkit-scrollbar, .app::-webkit-scrollbar, #root::-webkit-scrollbar {
     color: var(--primary-color);
     border-color: var(--primary-color);
 }
+
+/* Community submissions: the form, your own history, and the review queue. */
+.contribute-form { width: 100%; max-width: 34rem; }
+
+.contribute-count {
+    align-self: flex-end;
+    font-size: 0.7rem;
+    color: var(--sub-color);
+    font-family: 'JetBrains Mono', monospace;
+}
+
+.contribute-len.bad { color: var(--error-color); }
+
+.submission-list {
+    display: flex;
+    flex-direction: column;
+    gap: 0.6rem;
+    width: 100%;
+    max-width: 40rem;
+}
+
+.submission-row {
+    border: 1px solid var(--neutral-color);
+    border-radius: 8px;
+    padding: 0.75rem 0.9rem;
+    display: flex;
+    flex-direction: column;
+    gap: 0.4rem;
+    text-align: left;
+}
+
+.submission-head {
+    display: flex;
+    align-items: center;
+    gap: 0.6rem;
+    font-size: 0.7rem;
+    text-transform: uppercase;
+    letter-spacing: 1px;
+    color: var(--sub-color);
+}
+
+.submission-status { margin-left: auto; }
+.submission-status.status-approved { color: var(--primary-color); }
+.submission-status.status-rejected { color: var(--error-color); }
+.submission-status.status-pending { color: var(--warning-color); }
+
+.submission-content {
+    font-family: 'JetBrains Mono', monospace;
+    font-size: 0.85rem;
+    color: var(--text-color);
+    line-height: 1.5;
+}
+
+.submission-attribution,
+.submission-reason {
+    font-size: 0.75rem;
+    color: var(--sub-color);
+}
+
+.submission-reason { color: var(--error-color); }
+
+.submission-actions { display: flex; gap: 0.5rem; }
+
+/* Imported documents, kept between visits. Notes are worked through over
+   several sittings, so the list shows how far into each one you are. */
+.custom-library {
+    display: flex;
+    flex-direction: column;
+    gap: 0.35rem;
+    width: 100%;
+    margin-bottom: 0.5rem;
+}
+
+.custom-doc {
+    display: flex;
+    align-items: stretch;
+    gap: 0.35rem;
+}
+
+.custom-doc-open {
+    flex: 1 1 auto;
+    display: flex;
+    flex-direction: column;
+    align-items: flex-start;
+    gap: 0.15rem;
+    background: none;
+    border: 1px solid var(--neutral-color);
+    border-radius: 6px;
+    padding: 0.5rem 0.7rem;
+    color: var(--text-color);
+    font-family: inherit;
+    cursor: pointer;
+    text-align: left;
+    min-width: 0;
+}
+
+.custom-doc-open:hover {
+    border-color: var(--primary-color);
+}
+
+.custom-doc-name {
+    font-size: 0.85rem;
+    max-width: 100%;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+}
+
+.custom-doc-progress {
+    font-size: 0.7rem;
+    color: var(--sub-color);
+    font-family: 'JetBrains Mono', monospace;
+}
+
+.custom-doc-remove {
+    flex: 0 0 auto;
+    width: 2rem;
+    background: none;
+    border: 1px solid transparent;
+    border-radius: 6px;
+    color: var(--sub-color);
+    font-size: 1.1rem;
+    cursor: pointer;
+}
+
+.custom-doc-remove:hover {
+    color: var(--error-color);
+    border-color: color-mix(in srgb, var(--error-color) 45%, transparent);
+}