docs(inventory): remove leaked TBD comments

[RedZapdos123]

Description:

Issue #487 reported that placeholder public comments in inventory/inventory.proto were still set to TBD, and those placeholders were leaking into checked-in generated documentation and Swagger output.

MemoryInfo.total_usable_bytes had no real field description, and PCIeDeviceInfo still carried unresolved Type 9 or Type 41 ? text. Because these are public proto comments, the placeholders propagated into inventory/v1/autogen.md, inventory/v1/gen/go/inventory.swagger.json, and generated Go comments.

This PR replaces those placeholders with accurate wording:

• total_usable_bytes now explains that it is the usable memory capacity available to the system, not current memory usage.
• PCIeDeviceInfo now describes a single PCIe device discovered on the system instead of keeping unresolved placeholder text.

It also updates the checked-in generated documentation and generated Go comments so the public artifacts no longer expose TBD.

Closes #487.

Checklist:

• I have updated the source proto comments in inventory/inventory.proto.
• I have updated the checked-in generated documentation/artifacts affected by those comments.
• I have run buf lint.
• I have validated the proto compiles with protoc.
• I have verified the affected inventory files no longer contain the leaked TBD placeholders.

Before the fix:

inventory/inventory.proto still contained placeholder comments:

// TBD
int64 total_usable_bytes = 2;

// PCI device information
//  TBD: Type 9 or Type 41 ?
//  This structure describes a collection of PCI devices.
message PCIeDeviceInfo {

Those placeholders also appeared in checked-in generated artifacts, for example:

inventory/v1/autogen.md: total_usable_bytes ... TBD
inventory/v1/gen/go/inventory.swagger.json: "title": "TBD"
inventory/v1/autogen.md: PCIeDeviceInfo ... TBD: Type 9 or Type 41 ?

After the fix:

The source comments now describe the field and message directly:

// Total usable memory, in bytes, for this array.
// This is the amount of memory the system can actually
// use after accounting for reserved system memory.
// This is not the amount of memory currently in use.
int64 total_usable_bytes = 2;

// PCI device information
//  This structure describes a single PCIe device discovered
//  on the system.
message PCIeDeviceInfo {

The checked in generated docs and generated Go comments were updated to match, and the affected inventory artifacts no longer expose TBD.