Upgrade core dependencies to current stable versions

[chadhs]

Summary

Upgrades the Leiningen dependency stack from ~2019 pins to current stable releases, with compatibility fixes for Migratus/next.jdbc, Ring cookie keys, and Timbre’s Sentry appender. Also refreshes the README for local Java 17+ / Postgres setup.

Dependency upgrades

Area	From	To
Clojure	1.10.0	1.12.5
Ring	1.7.1	1.15.5
Compojure	1.6.1	1.7.2
ring-defaults	0.3.2	0.7.1
tools.cli	0.4.2	1.1.230
HugSQL	0.4.9	0.5.3
PostgreSQL JDBC	42.2.5	42.7.7
Migratus	1.2.3	1.6.7
Timbre	4.10.0	6.8.0
raven-clj	1.5.2	1.7.0
buddy-core	1.6.0	1.12.0-430
Hiccup	1.0.5	2.0.0
Garden	1.3.9	1.3.10
Cheshire	5.8.1	5.13.0
ring-webjars	0.2.0	0.3.1
Font Awesome	5.8.2	6.7.2

Compatibility / docs fixes

• Migratus uses {:jdbcUrl ...} for next.jdbc
• lein migrate runs the app --migrate CLI (works with -dev-main)
• Session cookie key converted to a 16-byte array
• Sentry appender loaded lazily from Timbre community namespace
• README: Java 17+, role-matched Postgres setup, local secrets, clearer run/test path

Test plan

• lein migrate exits cleanly
• lein with-profile test test — 28 assertions, 0 failures
• lein uberjar + jar --migrate / --help
• GitHub Actions CI green

Runtime note: Java 17+ required (Ring 1.14+/Jetty 12). CI uses Java 21.