Switch dependencies to compatible release (~=) specifiers (#651)

## Summary
- Replace `==` and `>=` version specifiers with `~=` (compatible
release) for all dependencies except `mcp[cli]`, which must remain
exact-pinned due to reliance on private SDK internals.
- Bumps minimum versions for `fastapi`, `uvicorn`, `starlette`, and
`filelock` to match currently resolved versions, avoiding conflicts with
`~=` constraints.

## Test plan
- [ ] `task check` passes
- [ ] `task test:unit` passes
- [ ] Verify `uv lock` resolves cleanly

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: DevonFulcher

.changes/unreleased/Under the Hood-20260316-113257.yaml

@@ -0,0 +1,3 @@
+kind: Under the Hood
+body: Switch dependencies to compatible release (~=) specifiers
+time: 2026-03-16T11:32:57.668349-05:00

pyproject.toml

@@ -28,23 +28,23 @@ classifiers = [
   "Typing :: Typed",
 ]
 dependencies = [
-  "authlib==1.6.7",
-  "dbt-protos>=1.0.431",
-  "dbt-sl-sdk[sync]>=0.13.2",
-  "dbtlabs-vortex==0.2.0",
-  "fastapi>=0.116.1",
-  "uvicorn>=0.31.1",
+  "authlib~=1.6.7",
+  "dbt-protos~=1.0.431",
+  "dbt-sl-sdk[sync]~=0.13.2",
+  "dbtlabs-vortex~=0.2.0",
+  "fastapi~=0.128.0",
+  "uvicorn~=0.38.0",
   # Pinned to a patch range because src/dbt_mcp/proxy/tools.py accesses private
   # MCP SDK internals (_tool_manager._tools, mcp.server.fastmcp.utilities.func_metadata).
   # When upgrading, verify those APIs are unchanged and update this pin accordingly.
   "mcp[cli]==1.26.0",
-  "pydantic-settings==2.10.1",
-  "pyjwt==2.12.0",
-  "pyyaml==6.0.2",
-  "requests==2.32.4",
-  "httpx==0.28.1",
-  "filelock>=3.18.0",
-  "starlette>=0.49.1",
+  "pydantic-settings~=2.10.1",
+  "pyjwt~=2.12.0",
+  "pyyaml~=6.0.2",
+  "requests~=2.32.4",
+  "httpx~=0.28.1",
+  "filelock~=3.20.3",
+  "starlette~=0.50.0",
 ]
 [dependency-groups]
 dev = [