feat(cli): replace deprecated generator aliases during fern generator upgrade

[iamnamananand996]

Description

Refs: User request from @iamnamananand996

fern generator upgrade now automatically replaces deprecated generator aliases (e.g. fern-typescript-node-sdk) with their canonical names (e.g. fern-typescript-sdk) in generators.yml. Previously, normalizeGeneratorName resolved aliases internally for version lookups but never wrote the canonical name back to the YAML file.

Link to Devin run

Changes Made

• upgradeGenerator.ts: After normalizing a generator name, compare the original (with org prefix) to the normalized result. If they differ (i.e. it's a deprecated alias), update the name field in the YAML. Preserves the user's format convention — if they used shorthand (fern-typescript-node-sdk), the replacement is also shorthand (fern-typescript-sdk); if they used the full form (fernapi/...), the replacement uses the full form.
• When the version is already latest but the name is a deprecated alias, the alias replacement is still applied and reported as an upgrade (rather than silently skipped as "already up to date").
• Updated CLI output to show alias renames: fern-typescript-node-sdk → fern-typescript-sdk: 1.0.0 → 1.5.0 or fern-typescript-node-sdk → fern-typescript-sdk: 2.0.0 (alias updated) when only the name changed.
• skippedMajorUpgrades messages also use the replaced canonical name for consistency.
• Added previousName optional field to AppliedUpgrade interface to track renames.
• Added new 3.77.0 entry to CLI versions.yml.

Testing

• Unit tests added — 3 new cases: alias replacement with version upgrade, shorthand format preservation, alias-only update when version is already latest
• All 7 existing + new tests pass
• Biome lint passes
• Local CLI build + manual test against a fixture with fern-typescript-node-sdk confirmed the alias is replaced in generators.yml and output shows fern-typescript-node-sdk → fern-typescript-sdk: 0.39.3 → 0.51.7

Review Checklist

• When latestVersion is null (e.g. API lookup fails), the alias name replacement is still written to the YAML (generator.set("name", ...) on L162) but no appliedUpgrade entry is recorded — verify this silent-rename-on-failure behavior is acceptable
• Confirm the new output formatting looks correct for all combinations (alias+version change, alias-only, version-only, no change)

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