Add a persisted test suite

`bundle exec rake test` (minitest, a default gem but pinned in
Gemfile for reproducibility) now covers what ad-hoc scripts kept
re-verifying by hand during development: Gpx/Fit/TrackStats parsing,
GpxStore/LiveTrackStore file/TTL logic, LiveTrackClient's payload
parsing, and app.rb's routes end to end via Rack::MockRequest.

MAPTOOL_DATA_DIR (new, app.rb) lets the suite point GPX_STORE/
LIVETRACK_STORE at a throwaway directory instead of real data/ —
without it every run would leave uploaded test files behind. Each
lib file's old `if __FILE__ == $0` self-check is now redundant with
real tests covering the same ground, so removed rather than kept as
a second copy of the same assertions. Wired into ci.yml so it isn't
just a local convenience.

Gemfile.lock

@@ -7,6 +7,7 @@ GEM
       version_gem (~> 1.1, >= 1.1.14)
     base64 (0.3.0)
     bigdecimal (4.1.2)
+    drb (2.2.3)
     faraday (2.14.3)
       faraday-net_http (>= 2.0, < 3.5)
       json
@@ -33,6 +34,9 @@ GEM
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     logger (1.7.0)
+    minitest (6.0.6)
+      drb (~> 2.0)
+      prism (~> 1.5)
     multi_json (1.21.1)
     multi_xml (0.9.1)
       bigdecimal (>= 3.1, < 5)
@@ -50,6 +54,7 @@ GEM
       rack (>= 1.2, < 4)
       snaky_hash (~> 2.0, >= 2.0.7)
       version_gem (~> 1.1, >= 1.1.14)
+    prism (1.9.0)
     puma (8.0.2)
       nio4r (~> 2.0)
     rack (3.2.7)
@@ -60,6 +65,7 @@ GEM
     rack-session (2.1.2)
       base64 (>= 0.1.0)
       rack (>= 3.0.0)
+    rake (13.4.2)
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
@@ -100,8 +106,10 @@ PLATFORMS
   x86_64-linux-musl
 
 DEPENDENCIES
+  minitest (~> 6.0)
   oauth2 (~> 2.0)
   puma (~> 8.0)
+  rake (~> 13.0)
   rerun
   rexml (~> 3.4)
   rubyzip (~> 2.4)
@@ -114,6 +122,7 @@ CHECKSUMS
   base64 (0.3.0) sha256=27337aeabad6ffae05c265c450490628ef3ebd4b67be58257393227588f5a97b
   bigdecimal (4.1.2) sha256=53d217666027eab4280346fba98e7d5b66baaae1b9c3c1c0ffe89d48188a3fbd
   bundler (4.0.18) sha256=02d9a17429de1847b4e0c9f27a9ee4b20c0a74c0a641b4e77195d6019e3618ac
+  drb (2.2.3) sha256=0b00d6fdb50995fe4a45dea13663493c841112e4068656854646f418fda13373
   faraday (2.14.3) sha256=1882247e6766615c8220b4392bf1d27f6ebb63d8e28267587cef1fb0bf37f278
   faraday-net_http (3.4.4) sha256=0e78af151747ed1b00f33e25973b4bc220d7f16c00c39676817c8b12331eb588
   ffi (1.17.4-aarch64-linux-gnu) sha256=b208f06f91ffd8f5e1193da3cae3d2ccfc27fc36fba577baf698d26d91c080df
@@ -131,16 +140,19 @@ CHECKSUMS
   jwt (3.2.0) sha256=5419b1fe37b1da0982bd07051f573a8b8789ab724c2aa7e785e4784a3ed217d7
   listen (3.10.0) sha256=c6e182db62143aeccc2e1960033bebe7445309c7272061979bb098d03760c9d2
   logger (1.7.0) sha256=196edec7cc44b66cfb40f9755ce11b392f21f7967696af15d274dde7edff0203
+  minitest (6.0.6) sha256=153ea36d1d987a62942382b61075745042a2b3123b1cd48f4c3675af9cc7d6f1
   multi_json (1.21.1) sha256=e6126a31808e3b4d19f483c775ceac34df190dffa62adfb63a165ee14ba68080
   multi_xml (0.9.1) sha256=7ce766b59c17241ed62976caeae1fae9b2431b263398c35396239a68c4a64e57
   mustermann (3.1.1) sha256=4c6170c7234d5499c345562ba7c7dfe73e1754286dcc1abb053064d66a127198
   net-http (0.9.1) sha256=25ba0b67c63e89df626ed8fac771d0ad24ad151a858af2cc8e6a716ca4336996
   nio4r (2.7.5) sha256=6c90168e48fb5f8e768419c93abb94ba2b892a1d0602cb06eef16d8b7df1dca1
   oauth2 (2.0.25) sha256=2f736a2f93c2caa67c1b08dc3c9889bb907d62643f3183fefaa1723cba6a82ac
+  prism (1.9.0) sha256=7b530c6a9f92c24300014919c9dcbc055bf4cdf51ec30aed099b06cd6674ef85
   puma (8.0.2) sha256=c8ed871dfbbe66448ea9ffd46692342d9804d4071522b52b5331b7b6e7b686fb
   rack (3.2.7) sha256=93e13e1c24f93556671d85d2d79fa228c3485815c50d7e2f265b5330c6528fb7
   rack-protection (4.2.1) sha256=cf6e2842df8c55f5e4d1a4be015e603e19e9bc3a7178bae58949ccbb58558bac
   rack-session (2.1.2) sha256=595434f8c0c3473ae7d7ac56ecda6cc6dfd9d37c0b2b5255330aa1576967ffe8
+  rake (13.4.2) sha256=cb825b2bd5f1f8e91ca37bddb4b9aaf345551b4731da62949be002fa89283701
   rb-fsevent (0.11.2) sha256=43900b972e7301d6570f64b850a5aa67833ee7d87b458ee92805d56b7318aefe
   rb-inotify (0.11.1) sha256=a0a700441239b0ff18eb65e3866236cd78613d6b9f78fea1f9ac47a85e47be6e
   rerun (0.14.0) sha256=996a5af2b2b34dcb30146c6c728addab9113e07c119003370daa9bf27feb88fd