Graceful error messages for project update validation failures

[dorkitude]

Problem

When linctl project update hits a GraphQL validation error (e.g., description too long), the error message is opaque:

❌ Failed to update project: GraphQL errors: [{Argument Validation Error [{3 4}] [projectUpdate]}]

This doesn't tell the user what actually went wrong or how to fix it.

Reproduction

linctl project update <project-id> -d "a description that is too long for Linear's field limit"

Expected behavior

A human-readable error message, e.g.:

❌ Failed to update project: description exceeds maximum length (250 characters)

Ideally linctl would parse known GraphQL validation errors and map them to friendly messages, with the raw error available via --verbose or similar.

[dorkitude]

Reviewed against current master after v0.1.12: the structural cause is still present. GraphQLError retains only message, locations, and path, so Linear error extensions—including a possible user-presentable validation message—are discarded before Execute formats the error.

The fix should be client-wide rather than a project-specific hard-coded length: retain error extensions, prefer Linear’s user-presentable message when present, and fall back safely to the GraphQL message. Please avoid encoding a 250-character limit unless it is verified against current upstream documentation. Add API tests for extension parsing/fallback plus a command test for the resulting project-update error.