fix: dev setup tweaks

[marthendalnunes]

Description

This PR:

• Makes make migrate report the latest migration dynamically instead of a stale hardcoded filename.
• Fixes WAYPOINT_HUB__SHARD_INDICES parsing to accept comma‑separated values (no brackets). This was broken: .env.example uses WAYPOINT_HUB__SHARD_INDICES=1,2,3, but Config::load() would fail with “expected a string for key HUB.SHARD_INDICES”. You can reproduce on main with "WAYPOINT_HUB__SHARD_INDICES=1,2,3 cargo run" and see the config load error. Adds a comma_separated deserializer and a unit test for it.

Type of change

• Bug fix (non-breaking change that fixes an issue)

Checklist

• I have read the CONTRIBUTING document
• My code follows the code style of this project
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly
• I have verified that my changes do not introduce regressions

[christopherwxyz]

@marthendalnunes I pushed a commit with some improvements:

Makefile fix:

• sort -V is GNU-specific and unavailable on macOS
• Replaced with sort which works since migrations use zero-padded numbers (001_, 002_, etc.)

comma_separated deserializer improvements:

• Use idiomatic serde lifetime naming ('de instead of 'a)
• Renamed inner enum from Value<T> to StringOrVec<U> for clarity
• Added doc comment explaining the function's purpose
• Added #[inline] attribute
• Use str::trim instead of closure

Test coverage:

• Added test for JSON array input: [1,2,3]
• Added test for whitespace-only string
• Added test for trailing/leading commas
• Added test for invalid value error message
• Consolidated into single test to avoid dead code warning

[marthendalnunes]

@christopherwxyz thanks for the improvements. All look good, I just added a few extra comma_separated tests for:

• Multiple consecutive commas (e.g., "1,,2,,3")
• Only commas (e.g., ",,,")
• Empty JSON array ([])
• Single element JSON array ([42])
• Negative number parsing error
• Overflow parsing error
• Single value as string (e.g., "42")