chore(lint): LeanCode's strict rules and a pre-push check

The workspace root's analysis_options.yaml includes leancode_lint 27 and enables its analyzer plugin (rules for blocs, Equatable and Flutter layout); the server and the app include that file, while the generated client keeps its own options. Plugins can only be enabled at the root of a pub workspace and only reach packages whose options include the root file, which was verified before settling on this layout. Most rules are warnings, casts, inference and raw types are strict, and the check treats infos as fatal too. lints and flutter_lints are no longer needed.

tool/check.sh checks formatting, runs dart analyze --fatal-infos and the server tests; .git/hooks/pre-push links to it, so every push has to pass it. AGENTS.md describes the checklist and how to install the hook in a fresh clone.

Fixes for the new rules: package imports, run() returns Future<void>, the server setup as one cascade, a primary constructor for the app widget, a const and a redundant argument. The workspace root keeps its conventional name `_` with a documented ignore.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

analysis_options.yaml

@@ -0,0 +1,11 @@
+# Lint rules for the whole pub workspace: LeanCode's strict set (leancode_lint), which
+# raises most rules to warnings and turns on strict casts, inference and raw types, plus
+# its analyzer plugin with rules for blocs, Equatable and Flutter layout.
+#
+# Analyzer plugins can only be enabled here, at the root of a pub workspace, and they only
+# apply to packages whose analysis_options.yaml includes this file. The server and the app
+# include it; the generated client keeps its own options, because it is never edited.
+include: package:leancode_lint/analysis_options.yaml
+
+plugins:
+  leancode_lint: ^27.0.0