chore: Update persona configuration structure and diff exclusions (#367)

Fix `.jp/config/personas/po.toml` to use `[assistant.system_prompt]`
instead of the top-level `[system_prompt]`.

Additionally, update `committer` and `stager` personas to exclude
`.jp/conversations` when executing `git diff-index`. This prevents
transient conversation state from being included in the diffs processed
by these personas, ensuring they focus on relevant code changes.

Also removes an inadvertent leak of a Google API key from the
conversation history. This key had already been rotated, but was still
present in the history, causing automated bots to keep notifying us of a
potential security breach.

This does highlight the importance of vetting conversation history
before committing it to a repository. We could potentially add a secrets
scanner to JP itself, allowing users to configure whether to rewrite,
error or warn when potential sensitive information is detected in
conversation history.

---------

Signed-off-by: Jean Mertz <git@jeanmertz.com>

Author: JeanMertz

.jp/config/personas/committer.toml

@@ -41,6 +41,7 @@ params.arg = [
     ".",
     ":^crates/jp_llm/tests/fixtures",
     ":^Cargo.lock",
+    ":^.jp/conversations",
 ]
 
 [style]

.jp/config/personas/po.toml

@@ -1,7 +1,7 @@
 [assistant]
 name = "Product Owner"
 
-[system_prompt]
+[assistant.system_prompt]
 strategy = "append"
 separator = "paragraph"
 value = """

.jp/config/personas/stager.toml

@@ -44,6 +44,7 @@ params.arg = [
     ".",
     ":^crates/jp_llm/tests/fixtures",
     ":^Cargo.lock",
+    ":^.jp/conversations",
 ]
 
 [[conversation.attachments]]

.jp/conversations/17653152345-agentic-shepherd-open-issues-list/events.json

@@ -100,7 +100,8 @@
                   "lines": 10
                 }
               },
-              "results_file_link": "osc8"
+              "results_file_link": "osc8",
+              "parameters": "json"
             }
           },
           "crate_readme": {
@@ -139,7 +140,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "off",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "agentic_shepherd_run": {
@@ -173,7 +175,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "off",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "cargo_expand": {
@@ -198,7 +201,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "off",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "cargo_test": {
@@ -223,7 +227,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "off",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "fs_create_file": {
@@ -292,7 +297,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "off",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "fs_grep_user_docs": {
@@ -318,7 +324,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "off",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "fs_list_files": {
@@ -349,7 +356,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "off",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "fs_modify_file": {
@@ -401,7 +409,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "off",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "git_commit": {
@@ -420,7 +429,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "full",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "github_code_search": {
@@ -633,7 +643,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "off",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "github_pulls": {
@@ -670,7 +681,8 @@
             "run": "unattended",
             "style": {
               "inline_results": "off",
-              "results_file_link": "full"
+              "results_file_link": "full",
+              "parameters": "json"
             }
           },
           "github_read_file": {