chore: add DeepSource config scoped to hand-written code (#96)

Enables DeepSource analysis on the repo. The SDK is mostly Fern-generated, so
generated surfaces (raw_client, client, socket_client, types, errors, core,
environment, package __init__) are excluded so findings focus on hand-written
code: crew, cli, helpers, tools, telemetry.

Python analyzer with mypy type checking (line length 120 to match ruff), plus
the secrets and test-coverage analyzers.

Author: abhishekmishragithub

.deepsource.toml

@@ -0,0 +1,38 @@
+# DeepSource config. Takes effect once the DeepSource GitHub app is activated on the
+# repo (it is). The SDK is mostly Fern-generated, so the generated surfaces are excluded
+# to keep analysis focused on hand-written code (crew, cli, helpers, tools, telemetry).
+# Analyzer reference: https://docs.deepsource.com/docs/platform/reference/core-analyzers
+# Tune exclude_patterns if the generated layout changes.
+version = 1
+
+exclude_patterns = [
+  "src/smallestai/**/raw_client.py",
+  "src/smallestai/**/client.py",
+  "src/smallestai/**/socket_client.py",
+  "src/smallestai/**/types/**",
+  "src/smallestai/**/errors/**",
+  "src/smallestai/core/**",
+  "src/smallestai/environment.py",
+  "src/smallestai/**/__init__.py",
+]
+
+test_patterns = [
+  "tests/**",
+]
+
+[[analyzers]]
+name = "python"
+enabled = true
+
+  [analyzers.meta]
+  runtime_version = "3.x.x"
+  type_checker = "mypy"
+  max_line_length = 120
+
+[[analyzers]]
+name = "secrets"
+enabled = true
+
+# test-coverage can be added once CI uploads a coverage report to DeepSource
+# (deepsource report --analyzer test-coverage). Left off until then to avoid a
+# perpetually-pending check.