fix(plugins): offer export formats the plugin manifest lists

[datlechin]

Why

• The Export dialog offered Parquet from a hand-coded entry because the v3 manifest had no exportFormatIds (fix(plugins): offer Parquet in Export until the manifest lists it #3508).
• The manifest's iconName was a third copy of each driver's icon; its only reader was the rejected-plugin row.

Change

• RegistryPlugin decodes databaseTypeIds and exportFormatIds as required and drops iconName. The Export dialog's install offers come from exportFormatIds only, and the dialog now observes the registry client so a late manifest fetch shows them (plugins-1).
• The Export menu label is the plugin's name: "Install Parquet Export…" instead of "Install Parquet…".
• A rejected plugin's icon comes from the curated snapshot of its primary type id, through one helper shared with the lazy plugin row (plugins-2).
• Fragment for feat(plugins): read the v3 plugin manifest from updates.tablepro.app #3503, which removed the com.TablePro.customRegistryURL setting without one.

Verified

• ExportFormatCatalogTests, PluginLazyRegistrationTests (new icon case), RegistryReleaseSelectionTests, PluginRegistryUpdatePassTests, RegistryClientFreshnessTests, DriverUnavailabilityTests pass. The hand-Parquet test became "no manifest offers no install"; the JSON fixtures gained exportFormatIds.

Not in this PR

• registry.py writing exportFormatIds and dropping iconName lands in its own PR. Both merge before v0.82.0-beta.1.
• Docs: docs(development): v3 manifest lists exportFormatIds, not iconName docs#39.