docs: add gateway-target documents five of eight target types, connector and web search are missing

## Description

`agentcore add gateway-target` accepts eight `--type` values at `main` (`31e98b7`), but the docs describe five. The three
missing from the docs are `connector`, `http-runtime` and `passthrough`. `connector` is the only way to add a managed web
search or Bedrock Knowledge Bases target, so web search reads as unsupported to anyone working from `docs/`.

The help string in the code lists all eight (`src/cli/primitives/GatewayTargetPrimitive.ts:278`):

```
Target type (required): mcp-server, api-gateway, open-api-schema, smithy-model, lambda-function-arn, http-runtime, connector, passthrough [non-interactive]
```

Three pages are affected:

- `docs/commands.md`, `add gateway-target`: says "Supports five target types" and the `--type` row lists five.
`--connector`, `--knowledge-base-id` and `--exclude-domains` are not documented anywhere on the page, although
`--connector ` is registered at `GatewayTargetPrimitive.ts:299` and `--exclude-domains ` at `:309`.
- `docs/configuration.md:493`: the `targetType` field is documented as `mcpServer`, `lambda`, `openApiSchema`,
`smithyModel`, `apiGateway` or `lambdaFunctionArn`. The schema also validates `connector`, `httpRuntime` and
`passthrough` (`src/schema/schemas/mcp.ts:746`, `:637`, `:681`), and a connector target carries a `connectorId` and a
`configurations[]` array that the page does not describe.
- `docs/gateway.md`: `README.md:228` sends readers here "for full target setup", and the strings `connector` and
`web-search` appear zero times in it.

`README.md:218` does document the web search target, so the README and `docs/` disagree with each other.

## Steps to Reproduce

1. Read the `add gateway-target` section of `docs/commands.md`.
2. Run `agentcore add gateway-target --help`.
3. Compare the `--type` values in each.

## Expected Behavior

The documented target types match the ones the CLI accepts, and `--connector`, `--knowledge-base-id` and
`--exclude-domains` appear in the `add gateway-target` flag table with an example for web search and one for Bedrock
Knowledge Bases.

## Actual Behavior

`docs/commands.md` documents five of the eight types and none of the connector flags. `docs/configuration.md` documents
six of the nine `targetType` values. `docs/gateway.md` does not mention connector targets at all.

## CLI Version

0.28.1

## Operating System

macOS

## Additional Context

Verified by reading the repository at `main` (`31e98b7`).

Web search itself is not gated. `src/cli/feature-flags.ts` checks `ENABLE_GATED_FEATURES`, and the only target type
still behind it is `passthrough` (`e2e-tests/httpgateway-all-targets.test.ts:74`). The connector path is covered by
`e2e-tests/web-search-lifecycle.test.ts` and `integ-tests/add-remove-web-search.test.ts`.

Web search did move in and out of a gate earlier this year (#1558, reverted in #1567, #1597, re-gated in #1625, tests
restored in #1711), which may be how the docs were left behind.

Start with the add gateway-target sections in docs/commands.md, docs/configuration.md, and docs/gateway.md, then compare them with src/cli/primitives/GatewayTargetPrimitive.ts and the schema references named in the issue. Review the existing README web-search example and the listed lifecycle tests. Done means all accepted target types and connector flags are documented, with web-search and Bedrock Knowledge Bases examples, and the three docs agree.

Written by the indexing model from the issue text.