fix(cli): support legacy generator names in IR definition

[iamnamananand996]

Description

Add compatibility for legacy generator names used in older IR configs by mapping fern-typescript and java-model to the current generator metadata. Also switch from getGeneratorNameOrThrow to normalizeGeneratorName (which returns null for unknown generators) so the CLI gracefully skips unrecognized generators instead of throwing.

Changes Made

• Add fern-typescript case to the TypeScript generator name mapping in getGeneratorVersions.ts
• Add java-model case (without fern- prefix) to the Java model generator name mapping
• Export new normalizeGeneratorName from @fern-api/configuration-loader
• Replace getGeneratorNameOrThrow with normalizeGeneratorName + null-check in getGeneratorVersions.ts (CLI upgrade utils), logging a debug message and skipping unknown generators
• Add CLI version 3.64.5 to packages/cli/cli/versions.yml
• Updated README.md generator (if applicable)

Updates since last revision

• Resolved merge conflict with main in versions.yml (main added 3.64.3 and 3.64.4)
• Rebased version from 3.65.1 → 3.64.5 to follow the correct sequence after main's latest 3.64.4

Testing

• Unit tests added/updated
• Manual testing completed

Human Review Checklist

• Verify version 3.64.5 is the correct next patch after 3.64.4 on main
• Confirm that silently skipping unknown generators (with debug log) is preferred over throwing — this is a behavioral change
• Check if any other legacy generator names (beyond fern-typescript and java-model) should also be mapped

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Link to Devin run: https://app.devin.ai/sessions/3c88c6585a1e4353becb41c8023583a0
Requested by: @iamnamananand996

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