Add Debian packaging, Makefile, manpages, tests, and design doc

Introduces a static-binary build and Debian package (amd64/arm64) with
version/commit/date stamped via -ldflags. Ships section-1 manpages for
ctool, ctfetch, and ctail. Adds a `version` subcommand reachable as
`ctool version`, `ctool -version`, `ctool --version`, `ctool fetch
version`, `ctool tail version`, and via the ctfetch/ctail symlinks. Adds
tests covering the dispatcher, fetch/tail argument parsing, and the
formatter/helper functions. Adds a retrofit design document modelled on
the vpp-maglev one, with FRs and NFRs for each tool and the dispatcher.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/ctool.1

@@ -0,0 +1,83 @@
+.TH CTOOL 1 "April 2026" "ctool" "User Commands"
+.SH NAME
+ctool \- tools for working with Static CT log tiles
+.SH SYNOPSIS
+.B ctool
+.I command
+[\fIflags\fR] [\fIargs\fR...]
+.PP
+.B ctool
+.B version
+.SH DESCRIPTION
+.B ctool
+is a busybox\-style front\-end for a set of tools that read tiles from
+a Static CT API log (c2sp.org/static\-ct\-api).
+It dispatches on the first argument to one of the subcommands below.
+The same binary can also be invoked through the
+.B ctfetch
+or
+.B ctail
+symlinks, in which case the subcommand name is implied by the link
+name; flags and arguments are unchanged.
+.SH COMMANDS
+.TP
+.B fetch
+Fetch and decode one or more entries from a Static CT log and print
+them as structured JSON. Supports both leaf\-index lookups and
+full\-tile dumps, with optional SCT decoding, issuer\-certificate
+lookup, and CT log\-list enrichment. See
+.BR ctfetch (1)
+for the full reference.
+.TP
+.B tail
+Follow a Static CT log. Polls the log's checkpoint, walks new data
+tiles as they complete, and prints a one\-line summary per certificate
+or precertificate \(em leaf index, type, validity range, issuer, and
+subject name. See
+.BR ctail (1)
+for the full reference.
+.TP
+.B version
+Print the binary's version, git commit hash, and build date, then
+exit. Equivalent forms
+.B ctool fetch version
+and
+.B ctool tail version
+also work and print the same information.
+.SH EXAMPLES
+Fetch a single leaf entry with all optional enrichments:
+.PP
+.RS
+.EX
+$ ctool fetch https://halloumi2026h1.mon.ct.ipng.ch 629794635 +all
+.EE
+.RE
+.PP
+Tail a log from the current tree tip:
+.PP
+.RS
+.EX
+$ ctool tail https://halloumi2026h2.mon.ct.ipng.ch
+.EE
+.RE
+.PP
+Print the build version:
+.PP
+.RS
+.EX
+$ ctool version
+ctool version 0.1.0 (commit abc1234, built 2026\-04\-21T12:00:00Z)
+.EE
+.RE
+.SH "FULL DOCUMENTATION"
+This manpage is an overview only. For the complete reference of each
+subcommand \(em every flag, every output modifier, and the format of
+the JSON and tail\-line output \(em see the per\-command manpages:
+.BR ctfetch (1)
+and
+.BR ctail (1).
+.SH SEE ALSO
+.BR ctfetch (1),
+.BR ctail (1)
+.SH AUTHOR
+Pim van Pelt <pim@ipng.ch>