[feat](trx-rs): keep a station log, and a layout to work the bands from

The logbook of issue #54, in the shape the proposal settled on.

A new crate, trx-logbook, holds the contact, the ADIF reader and writer, the
file, and the rules for telling one contact from two.  ADIF because it is the
only thing the ecosystem reads: LoTW, eQSL, Club Log, QRZ and every other
logger take it and nothing else, so a log that cannot write .adi cannot be
uploaded, confirmed or moved.  The reader is forgiving in the ways real files
are irregular -- lowercase tags, CRLF, missing header, unknown fields, a
declared length that is the only thing ending a value -- and carries what it
does not model through to the export, so a round trip does not strip what
another program wrote.

The file is JSON Lines, appended one line per contact.  A log is the one
thing here that cannot be regenerated, and the bookmark store's whole-file
dump would rewrite megabytes to log one contact and lose all of them if the
power went halfway; an append costs the record being written and no more,
which a test tears a line in half to prove.  Edits append revisions, deletes
append tombstones, and the file compacts when the superseded outnumber the
live.

The panel is its own tab and stands in every layout.  An entry opens with six
fields and no more -- frequency, mode, rig name, time, and the callsign and
locator of whatever decode it was started from.  A report stays empty: an FT8
SNR is not what was sent.  Times come from the server, because the browser
may be a phone in another timezone, and the panel says so when the two
disagree by more than a second.  Worked-before answers as a callsign is
typed.

A decode is not a contact, so the Log button on an FT8 or APRS row opens an
entry and logs nothing by itself.

The ham layout is the fifth operator layout, opening on the logbook with the
radio controls around it, offered only where the rig can transmit.

Two bugs found on the way, both in code written here: a frequency of a whole
number of megahertz ending in a zero rendered as a tenth of itself, in Rust
and in TypeScript alike, because trimming trailing zeros from "20.000000"
walks back through the point.  The API also sits under /api/logbook rather
than /logbook, so it cannot shadow its own page the way /bookmarks does.

Closes #54

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SyX26FCpMQxiBoC7r5K1A7
Signed-off-by: Stan Grams <sjg@haxx.space>

docs/User-Manual.md

@@ -477,6 +477,57 @@ Each browser tab keeps its own selection, so two tabs can watch two rigs.
 
 ---
 
+## Logbook
+
+The **Logbook** tab keeps the station's contacts and speaks ADIF, so a log can
+be uploaded to LoTW, eQSL, Club Log or QRZ, or moved to another logger.
+
+An entry opens pre-filled with six fields and no more: the frequency, mode and
+name of the rig you are on, the time from the server's clock, and — when the
+entry was started from a decode or a map station — that station's callsign and
+locator. Signal reports, name, comment and the rest are yours to fill in; a
+report in particular is never guessed, because an FT8 SNR is not what was sent.
+
+Your own callsign and locator are not per-contact fields. They are station
+identity: the callsign comes from `[trx-client.general].callsign`, the locator
+from the rig's position, and both are shown once at the top of the panel. The
+operator defaults to the station callsign and can be changed for the session,
+which is what a multi-operator station needs.
+
+**Times are the server's**, in UTC — the server is the machine at the radio. If
+the browser's clock disagrees by more than a second the entry says so rather
+than logging a time you did not expect.
+
+**A decode is not a contact.** The decoders are receive-only, so a **Log**
+button on an FT8 or APRS row opens an entry with what was heard in it and logs
+nothing by itself. Digital QSOs made in WSJT-X come in through Import ADIF, the
+way every other logger takes them.
+
+| Action | What it does |
+|--------|--------------|
+| Log contact | Writes the entry and opens a fresh one |
+| Export ADIF | Downloads the log — filtered, if a filter is set |
+| Import ADIF | Reads a file, skipping contacts already held and reporting what could not be read |
+| Worked before | Shows, as you type a callsign, which bands and modes it has been worked on |
+
+Two contacts are treated as the same when the callsign, band and mode match and
+the times are within two minutes: two loggers rarely stamp a QSO to the same
+minute, one recording when it started and the other when it was typed.
+
+The log is a JSON Lines file, appended one contact at a time so a crash costs at
+most the contact being written. It lives in your data directory by default;
+`[trx-client.logbook].path` moves it, for a station that keeps its log on a
+backed-up volume.
+
+### Ham radio layout
+
+The **Ham radio** operator layout opens on the logbook with the transceiver
+controls around it — the arrangement for working the bands, where logging the
+contact is the task and the radio is the instrument. It is offered only where
+the selected rig can transmit; a receiver has no contacts to log.
+
+---
+
 ## Tune Links
 
 Every page of the web UI carries what the radio is doing in its address, so the