feat(config)!: one ordering for configuration sources, and a bootstrap deny rule

$DSH_HOME/.env had just become an ordinary environment layer, which left the
harness resolving user-facing values from a flattened process.env that could
no longer say where a value came from. A key stored through the web page
stayed shadowed by an older key in the user's own .env. An endpoint could be
redirected by the project: the invoking directory's .env is materialized like
every other layer, and a base URL decides where a resolved API key is sent, so
a DEEPSEEK_BASE_URL written into a model-editable workspace would send the
user's credential — and the prompts carrying their code — to whatever host
that file named.

Give every user-facing value one ordering, with four kinds of source:

  explicit for this run     per-operation override, CLI argument
  > authored by deployment  --config / --config-replace
  > this launch's shell     inherited process environment
  > product-managed store   settings.yaml, .credentials.yaml
  > discovered file         $DSH_HOME/.env
  > defaults                schema default, shipped base, public default

The domains differ only in which tiers exist. The earlier split — credentials
ranking the environment over the managed file while settings ranked over the
environment — was inconsistent: the distinguishing fact is who authored the
source, not the domain.

packages/util/environment owns an immutable snapshot with per-layer
provenance. getFrom(name, sources) searches only the layers a caller names,
and omitting one is a refusal rather than a demotion: the adapters ask for
['process', 'user-env'], so no reordering can let a project file back into a
decision it was excluded from.

isBootstrapOnly rejects, before anything is materialized, any .env setting a
variable that governs how a process launches (PATH, SHELL, NODE_OPTIONS,
LD_PRELOAD), where code or model-visible instructions load from (the whole
DSH_* namespace, HOME, XDG_*), or how the network is reached (proxy and CA
variables). The namespace is denied wholesale so a switch added later cannot
become settable by being forgotten, and there is no opt-out.

verify-config-source-ownership keeps both rules: no unregistered process.env
read under packages/*/*/src (26 allowlisted with reasons), and no apiKey,
baseURL, or headers inlined from the environment in shipped Cordis config —
removing those inlines is what makes the deployment tier meaningful.

docs/config-catalog.md

@@ -423,7 +423,7 @@ export interface Config {
 }
 ```
 
-Source: [`packages/credentials/credentials-local/src/index.ts:35`](../packages/credentials/credentials-local/src/index.ts)
+Source: [`packages/credentials/credentials-local/src/index.ts:54`](../packages/credentials/credentials-local/src/index.ts)
 
 ## `@deepseek-ai/dsh-fs-local`
 
@@ -632,7 +632,7 @@ export interface Config {
   apiKey?: string
   /** Credential reference (environment-variable name) resolved per request; defaults to `DEEPSEEK_API_KEY`. */
   apiKeyEnv?: string
-  /** Endpoint base; falls back to $DEEPSEEK_BASE_URL, then the public API. */
+  /** Endpoint base; falls back to $DEEPSEEK_BASE_URL from a trusted environment layer, then the public API. */
   baseURL?: string
   /** Deployment thinking policy; `disabled` limits every conversation request to `off`. */
   thinking?: 'enabled' | 'disabled'
@@ -665,7 +665,7 @@ export interface DeepSeekCatalogModel {
 
 Depends on: [`RetryPolicyConfig`](../packages/llm/llm/src/index.ts)
 
-Source: [`packages/llm/llm-deepseek/src/index.ts:60`](../packages/llm/llm-deepseek/src/index.ts)
+Source: [`packages/llm/llm-deepseek/src/index.ts:61`](../packages/llm/llm-deepseek/src/index.ts)
 
 ## `@deepseek-ai/dsh-llm-pi-ai`
 
@@ -2229,7 +2229,7 @@ export interface Config {
 }
 ```
 
-Source: [`packages/web/web-search-deepseek/src/index.ts:43`](../packages/web/web-search-deepseek/src/index.ts)
+Source: [`packages/web/web-search-deepseek/src/index.ts:44`](../packages/web/web-search-deepseek/src/index.ts)
 
 ## `@deepseek-ai/dsh-web-search-exa`
 
@@ -2251,7 +2251,7 @@ export interface Config {
 }
 ```
 
-Source: [`packages/web/web-search-exa/src/index.ts:37`](../packages/web/web-search-exa/src/index.ts)
+Source: [`packages/web/web-search-exa/src/index.ts:38`](../packages/web/web-search-exa/src/index.ts)
 
 ## `@deepseek-ai/dsh-web-search-perplexity`
 
@@ -2273,7 +2273,7 @@ export interface Config {
 }
 ```
 
-Source: [`packages/web/web-search-perplexity/src/index.ts:31`](../packages/web/web-search-perplexity/src/index.ts)
+Source: [`packages/web/web-search-perplexity/src/index.ts:32`](../packages/web/web-search-perplexity/src/index.ts)
 
 ## `@deepseek-ai/dsh-workflow-workerthread`
 
@@ -2417,6 +2417,7 @@ Imported as libraries by other packages; a `cordis.yml` cannot load them.
 - `@deepseek-ai/dsh-client-ui-slots` ([`packages/client/ui-slots/src/index.ts`](../packages/client/ui-slots/src/index.ts))
 - `@deepseek-ai/dsh-client-web` ([`packages/client/web/src/index.ts`](../packages/client/web/src/index.ts))
 - `@deepseek-ai/dsh-client-web-react` ([`packages/client/web-react/src/index.ts`](../packages/client/web-react/src/index.ts))
+- `@deepseek-ai/dsh-environment` ([`packages/util/environment/src/index.ts`](../packages/util/environment/src/index.ts))
 - `@deepseek-ai/dsh-helper` ([`packages/sdk/helper/src/index.ts`](../packages/sdk/helper/src/index.ts))
 - `@deepseek-ai/dsh-hook-protocol` ([`packages/hooks/hook-protocol/src/index.ts`](../packages/hooks/hook-protocol/src/index.ts))
 - `@deepseek-ai/dsh-jsonrpc-demo` ([`packages/examples/jsonrpc-demo/src/index.ts`](../packages/examples/jsonrpc-demo/src/index.ts))